How should I consider a possibly rude reply from a potential PhD advisor?

He/she is probably very busy, and has repeated the same message probably N times. Also, we all assume students will find the required information by themselves. Nowadays, I find that students simply don't spend the time to look for information. Their first instinct is to simply to message me, and hope that I will solve their problems for them; this is very similar to a kid asking their parents, can you please clean up after me? It is ok if you are 2 year old, but not OK after a certain age.

As for whether the professor should be a supervisor, you should look at whether he/she is successful in supervising students. Yes, he/she may not entertain trivial questions and tell you off, but that may mean you need to work independently and at a high level.

As an external observer, what strikes me here is:

A) yes, the answer is unnecessarily rude. Everybody can have bad days, but if this person routinely reacts aggressively and loses their temper whenever dealing with perceived "failures" from others, then they seem a poor match as an advisor for you, as they probably would continuously drag you down emotionally.

So the bigger question here is: is this a pattern of behaviour, or is this person usually supportive? Do they encourage other people, or constantly put them down? Basically: are they a bully? Open your eyes and ears and look for further clues. And maybe talk to some of their current or former students.

B) Poor organisation/communication skills. Important information like a schedule shouldn't be communicated through a chat box, or require attendance to a specific event. You would expect it to feature very clearly in some easily accessible reference written material (a web page for the course, and/or the course's introduction slides, etc.)

That's another red flag. Again, does this person seem generally well organised, do they communicate their thoughts clearly, or do they generate an aura of confusion around them, and expect other people to just read their minds? (and blame them when they fail to do so). Again, try and talk to some of their current and former students...

That second point would be the biggest red flag for me. You can grow a thick skin against insensitive comments, but you can't really work around a disorganised advisor who can't communicate.

of the course I am auditing

One possibility is that you have (a) an overworked professor, (b) who gets asked little questions like this over & over enough to get annoyed and who (c) appreciates these questions even less from someone who is only auditing the course.

As I understand it (having been out of college for a very long time, but Google'd it to be sure it is still at least basically what it meant 35 years ago), auditing means you are not getting credit for the course. If the professor recognizes that you are only auditing the course, then they may well treat your questions, especially about things like project scheduling, as almost pointless since you don't have to actually do the projects!

Your intention in auditing may be to do everything in the course at a top level, as if you were taking the course for credit. But at least some people audit so they can learn the subject matter without being under any pressure and, therefore, not bother with exams and projects.

If indeed that is the case, I would expect the professor to (time permitting) respond well to a subject-matter question from you, just not to the administrative questions.