My guess is that the question might've been referring to the Bills first win over a team that came from the NFL and not the AFL. But I'm honestly too tired at the moment to check through the stats to see if the Bills lost to every original NFL team they faced until that win against the Lions in '79 to see if my theory is right. As far as I'm concerned, your answer is correct based on how the question is phrased. I've forwarded this on to Admin because if it's intending to be something more tricky, which I assume it is since it's a 175 pointer, the wording doesn't reflect it.