Doh! You're right, I didn't look closely enough.
When I looked in my archives, I found I have some pics of a 1999 vintage Eotech - I'm guessing this was the first model marketed by Eotech. It looks like yours is missing the protective hood, and I don't think they came with the archery sights.
This one has windage and elevation adjustments on the back and side, as you can see in the pics below, and yours definitely doesn't have that extension at the back with the adjustments. I'm thinking it is an archery version, and is adjusted with the mount, rather than the screws - the Eotech 520 archery sight has a micro windage adjustment, but recommends a mount with elevation and coarse windage adjustments.
ETA - I found this page from the internet wayback machine:
http://web.archive.org/web/20010607005025/www.eotech-inc.com/archery/mainframe.html
It shows the Model 420 archery sight has no windage adjustment, while the 520 (the current form factor) has windage only and is shorter than the 420. I'm starting to think yours is a late model 1st gen, right before they changed to the 2nd gen that looks like the current ones.
Unfortunately, I don't remember where I got these from - probably here or another gun board. The label is washed out in the pic, and I can only get Manufactured March - Serial 699xx out of it.
If you do find some info on it, be sure to post it back here.