この質問に回答する前に、まず先生の答えが間違ってるような気がするのは気のせい?
佐藤さんが木村さんを待ってあげた。
佐藤さんが木村さんを待ってくれた。
Both says, "Sato waited for Kimura." There is a difference between the two though.
I can't say much, but I suppose there should be some reason that explain this matter. If you had the exact question, someone would have explained clearly, I suppose. Sorry.