I have seen people assume a question with no system information at all was D&D, but that's a different scope. We see it a lot in
system-agnostic and
social questions where people tend to assume the game is D&D, or works like D&D, or that the solutions that apply to D&D will definitely apply there with no issues. Sometimes they'll do it
in spite of the question making it clear what the system was and that it wasn't D&D.