Is this guy a good teacher?

ANSWER: I think he's a great teacher.

But I think he mistakenly explained 맞히다, which really means ""to  guess or do something correctly," not "to make something correct." For example, the sentence "정답을 맞혀봐요," means "Try to guess the correct answer," not "Try to make the correct answer."

In his spoken explanation he does say, "to guess something correctly," but the writing on the screen is "to make something correct," which is wrong.

So, the verb 맞히다 means "to guess or do something correctly," including "hitting a target," and the verb 맞추다 means "to match something" or "to fit something," which often requires some adjustment.