That's not a good translation imo. Though it is literally saying "in the University", it would be understood as "in University" (probably the one the speaker typically attends). "In a university" seems like a mistake to me. Gaelic does the same for e.g. school: "Tha mi anns an sgoil" = "I am in school".
Edit: Either the sentence linked used to say "anns an" and has been fixed, or I completely imagined it. As it is now, it's correct.
The sentence above? There has been a weird bug I've noticed where sometimes the EN>GD translation doesn't match the GD>EN one, but usually that has to be fixed manually. Tha mi anns an oilthigh isn't a sentence that's taught on the course, so either there was a bug that fixed itself, or you imagined it :D
Also if the sentence had been fixed, usually the thread disappears. We would still be able to find it because we've commented on it, but it would disappear from public view because it would no longer be attached to a sentence, if you get me?