Well, I don't know what was the purpose of the question and maybe it really was sufficiently and correctly answered.
But I do not think the answer is that simple. As there are for example treacheries that specifically target either exhausted characters or characters committed to a quest, which is not the same (e.g. you can have a character that's committed to quest, but is ready due to some effect - e.g. Aragorn or using Unexpected courage).
Any situation in the game comes with the caveat, "barring card text." Cards can always change the situation.
Barring card text, a character is exhausted by questing, defending or attacking.