Harry debated running off when the girl came storming over to him because despite his size he knew better than to underestimate an angry woman. And this young woman was really, really angry with him. The only reason he didn't run off was because that would look really suspicious and he didn't want to leave her alone after she just had a run in with a vampire.

When she started telling him off for just a moment he thought maybe he's be better off if he DID leave her. She was really angry at him for... saving her life?

"What are you talking about I only burned the monster. And I'm following you because you're wandering around in a cemetary at night, which is really dumb. And it's a good thing I was because I don't know if you noticed but you were about to be attacked by a vampire. Which, that should actually freak you out more than a guy saving you from one."

Harry didn't mean to get riled up but he couldn't help but match her energy with her being so upset. The small part of his brain that clearly did not care about survival pointed out that she looked even more attractive all riled up but he squashed that part down. So not the time for that.