MC has super hearing. Eventually upgrades his Super Hearing to the point where he learns magic just by hearing of the magic. He's in an isolated tower in the middle of fuck all nowhere. Likely he is listening to magic being discussed in faraway towns, maybe even wizard towers isolated from society. Basically he's listening in on at least a general country wide area to learn all sorts of magic. But he describes it himself as The World.
Somehow did not listen in on all sorts of taverns, inns, shops, adventurers having small talk and learned about the general history, standards, slangs, common sense and general know-how of the world.
OK.