Someone (Aさん) asks a question on a forum. Bさん provides an answer. I see the answer as incomplete, so I correct Bさん and provide some supplementary information. Aさん, the OP, replies to me:
I thought that was the end of it. But then Bさん says back to me:
I am thrown by this response. I don't know what Bさん is trying to say or if they are displeased because I corrected them (not the first time). What does 打つ mean here? "It didn't occur to me"? What's also off about that response is everybody is very polite on the forum, basically 敬語 all the way. Bさん too, except in this one repsonse to me. えっため口？なんで？俺、何か悪いことした？ That's how I feel. So what do they mean?
A little more background: it is a math question. The correct answer includes two possibilities, and Bさん only gives a number based on one of the possibilities. I complement their answer by showing another possible option.