You guys should remember the 2.5 gallon preaching on this forums isn't for space requirements, it's because most people can't take care of a smaller tank properly, with it's daily water changes.
So, as long as it's well cared for, I think it'll be ok.
How's the temperature looking, though? 78-80 degrees is ideal, and you'd need to get a 2.5gallon to be able to heat it properly.
Cute tank, though, he seems pretty happy.