Agreed about #3. The person has every reason to think that prompt was okay. Treating them like they stepped out of bounds when they didn't can be hurtful and make people feel bad.

It's important to have the rules set up solidly ahead of time.

I am not the prompter, but speaking from personal experience elsewhere if I have comments deleted that I thought were okay I feel really bad. Like I've crossed some unwritten rule that I should somehow have known. I feel like a reject, like I never was part of that community / fandom / etc.