Have you completely missed where GoDaddy explicitly informed Goatboy/AR15.com that they had suspended the account, effective immediately, claiming the site hosted illegal activity?  Or that the reason things are working now is that Goatboy moved the domain registration to another provider, in addition to setting up a new domain name?  Your speculation about misconfiguration does not match the known facts.

OK, I'll try to give a more complete explanation hopefully without devolving into technobabble.  I'm not an expert on DNS, but I have built the internal DNS servers for a large chunk of a major corporation known for jet engines, appliances, and, at the time, financial services, so I have had my hands in the guts of it before :-)

Some basic acronyms:

DNS - Domain Name Services - a directory service associating domain names with IP (internet protocol) addresses
SOA - start of authority - this is at the heart of what happened today, it's a basic building block for the entire Domain Name Services system.
TTL - Time-to-Live - how long a DNS server hangs on to a particular record before it queries back to a higher server that ultimately checks with the SOA
"root domains" - these are your .com, .gov, .info, .biz, etc... domains.

When you register a DNS name through a registrar, they publish a record to the appropriate DNS servers that includes who the SOA is for the domain, what IP addresses to associate with the domain, what mail servers/exchangers (MX) to use when sending email to the domain, and some other bits of information.  When you try to go to a site on the internet, your computer asks the DNS servers it's configured to use (usually the ones your Internet Service Provider, such as Comcast, Cox, Verizon, etc maintain) for the IP address associated with the host or domain name in question, those DNS servers in turn query other DNS servers higher up the pipeline, eventually landing at the root servers, to get that address if they don't already have it in their own database.  Entries in their databases are retained based on their time-to-live (TTL), after which point they are dumped out and queried anew when a client requests the information.  

What GoDaddy did was tell those DNS servers that the domain "ar15.com" was suspended, so they started returning "site not found" errors when users attempted to access it.  Different DNS servers had different TTL settings, so those that updated more quickly weren't allowing access to the site earlier than those that didn't update as quickly.  If Goatboy hadn't managed to transfer the domain registration to a new registrar quickly, if, for example, GoDaddy had insisted on the full five days allowed by policies set by the international board that controls DNS registries (ICANN), access to the site could have been down for five to six days before a new registry entry was recognized by all of the DNS servers out there.

Some commands people have referenced on this topic:
ping - a simple tool that sends a UDP (user datagram protocol) packet to a host to see if it responds, UDP traffic is "fire and forget", there is no requirement that a receiving host acknowledge receiving it, and turning off UDP traffic is fairly common in the security world.
traceroute/tracert - a tool that queries all of the "hops" between the sending host and the targeted host using UDP packets, used for troubleshooting network communication errors by showing where the UDP packets start failing (if routing protocols say there should be 14 hops between the two hosts, but all the packets are dying when sent to the 11th switch along the way, you usually try to figure out why that switch isn't responding properly as part of troubleshooting the network issues).
nslookup - an older tool for querying the DNS servers to find out what information exists for a host or domain name, some Linux distributions have phased it out in favor of "dig".
BIND - Berkeley Internet Name Daemon - standards and software developed in the early  1980's to manage domain name resolution, BIND (also known is named) is the most common Domain Name System software in use (my project at the unnamed major corporation was moving one of their major subdomains to a standard BIND implementation on UNIX from a custom commercial version that was no longer supported).  
WHOIS - a database of domain name ownership and registries (which is itself split up, tracking down a particular host may require checking multiple WHOIS servers, the root server will tell you which one to check, which may point you to yet another server).  This will include information such as when a particular domain name was registered with that registrar, who to contact for problems at that domain, how long their registration is valid, etc...

True, in trying not to get TOO technical, I let some inaccuracy in.  As noted, I'm not primarily a DNS guy, haven't had to dive into the guts in over a decade, if not two :-)

It's a certificate issue, likely with the browser.  Something isn't quite in sync yet.