This is not about IF he taught but about his teaching skills, HOW he taught.
Maybe. So how do you find out? I've answered already with my opinion of HOW. But for those who want to find out they would probably want to look at WHERE, WHEN, WHAT, IF, TO WHOM, HOW OFTEN, WHO UNDERSTOOD, WHO DIDN'T, WHY......... ETC.
Ha, ha, Why? is an interesting question. Why did he teach? If you don't know the answer to that then how can you judge his ability fairly?