@lolmaolol He might already know more than the faculty about magic, but that doesnt have to mean that what he knows encompasses all that they know (particularly as his research was focused on whatever he called his hoi hoi magic). He already found out about swift magic staves, something he had no idea of. So makes sense if he can learn a lot more techniques that diverged in another direction than his research, 5000 years ago. It is also unlikely he, who had no talent for magic, would outpace the research of the entire world. So the techniques that has been researched is likely pushed further than he could have himself. This is shown in that he had trouble with a mere chimaera (only managing to defeat it by using a pre-prepared tool called dynamite. Which makes me worried if his 5k-years-researched offensive magics cant even beat a few sticks of undirected dynamite.), something your average S-ranked adventurer would defeat with laughable ease even when caught unprepared. And there are quite a few in that country alone, and iirc all archmages and the melee equivalents were considered s ranked.
And even aside from all that, learning at school will teach him what is considered "normal" magic, allowing him to stand out less if he ever wishes to. Also likely that graduating a school will remove the Fool title. Iirc both were the actual reasons he hyped for school originally.