For Harry, is morality about intentions or consequences? Maybe he doesn't care whether Dumbledore did it deliberately; if anybody is so careless as to do such a thing accidentally, then they're an enemy.

It's hard to tell. Harry's morality seems to be somewhat ad-hoc in nature. For example, he declares that sometimes killing is necessary but torture can never be, which rules out being purely consequentialist but is hardly typical of deontological ethical frameworks either (but fairly normal for standard human thinking).

Even so it would surprise me if Harry didn't distinguish at least partially on intent. Completely not caring about intent, well, just "doesn't seem like his style". I observe, for example, that Harry judges Dumbledore for sharing gossip to Severus with the intent of setting Voldemort after Harry's family. When looking at raw causal interactions there are no doubt countless trivial actions that have the consequence of really bad things happening. Yet Harry singles Dumbledore's (alleged) conniving out purely based on the fact that he intended it to lead to particular a chain of events.