You're absolutely right. OP's behaviour is a major red flag in my book.

I was stalked by a fellow pupil during my the first year of my undergraduate degree. It was in person at first, but after he was reported to the head of our course, it transferred to mostly online. The kicker is, we used to be friends. But I gently rejected him because I already had a boyfriend, and he accused me of lying about it, so he started harassing me. Thinking he was owed information.

He'd trawl through my Facebook for hours, and send messages about possibly inconsistencies in my life, or exes of mine, or things I said 6 months ago, one year ago, five years ago. He used a trauma of mine, the murder of my aunt (which happened only a few years before that point of my life) as a "gotcha" moment because I hadn't explicitly told him about it in detail. He kept demanding information about her murder, and at the time I was still fresh from the trauma, and didn't want to share it with anyone. Anyway, when he was reported again to the Dean and to the authorities, one of his excuses was "it's just Facebook! It's not real stalking [anymore]!" as though he thought this kind of behaviour was okay, just because it was online.

Anyway, maybe I'm oversensative due to my past experiences, but OP's behaviour really triggered that fight or flight response. He ignored her boundaries, and went trawling through Facebook to dig for private information about her that she was, at the time, totally (and quite reasonably) unable to share with her. It's a huge violation of trust and personal space. I'm not saying OP is going to go as far as my stalker did, but I think he needs to look at how he handled this situation, learn from it, and improve his behaviour going forward.