I think this issue cuts both ways.
I do not want to address this specific situation, but rather a generalization of it.
I think we should all strive to keep our communication as gentle and professional as possible. That does not mean there is no place for lighthearted remarks or attempts at humor, but we have to be cognizant of the medium of communication as well.
The FAQ already addresses this, but here are some additional thoughts on the matter.
- Civility and respect should be the norm. We have users of all ages, occupations, and levels of mathematical sophistication. Many come here to learn, others to teach, and a few are here for a bit of both. There is no reason we should treat people any differently than we would in a face-to-face conversation, or, with even more care (see below). If I'm ever wondering if I should make a particular comment or remark, I try to think whether I'd be willing to say it in the same way to a colleague that had come in and asked it in my office. We obviously won't always get this right, but I feel we should try.
- Commenters deserve the benefit of the doubt. None of the usual audiovisual cues in human communication are attached to the comments we make. Even for those that try hard at it, it is, thus, extremely difficult to get the tone of comments perfect at times. This is particularly true here since there is also a 600 character limit, which biases everyone towards shorter and more direct communication. As mathematicians, we're also more keen on precision and correctness, leading some comments to appear too direct or even rude. That's rarely the intent, and we should keep that fact in mind.
If you think something sounds rude or sarcastic try to step back and see the comment in the best light possible. If you can see a way in which it could have been said in a neutral tone, that's likely how it was intended and at the very least should be the default interpretation over another one in which you would take offense.
- Social correction is important. This is a community and with any community come norms and standards. We expect a certain kind of behavior out of both new users and old. If someone is behaving in a disruptive way, I feel it is the duty of the community to step in and let a user know that they've stepped out of bounds. A moderator sometimes has the appearance of more authority and so users are likely to be more responsive to them. That said, as front-line representatives of the community, moderators, in particular, should strive to always be as tactful and professional as possible.