Agree with all you've said but I think the question that was put to him was poorly worded. It didn't need to mention starting Michael Keane, it should have just asked why O'Brien didn't start. As soon as the journalist suggests Keane shouldn't have started over O'Brien, Dyche is jumping to his defence/justifying his team selection. He'd do the same for most if not all players I think.
Wouldn't read too much into it and hopefully next week, if it's a choice between the two, he makes the decision we all want to see.