The short answer to your question is: yes, the characters in Among Us are astronauts. What else would they be? They’re flying through space and other planets doing meaningless tasks and killing each other.
Who else does that? Canadians?
If you look at the concept art from the Among Us devs, you wonder if anyone would confuse them for anything else.
Actually, if you look really closely at the one at the top right, then maybe you could confuse them for a starfish. However, the developers decided instead of having obvious hands, the astronauts in Among Us would have floating hands come out of nowhere to do tasks and snap each other’s necks.
At least there are people who are using their amazing artistic skills to make the Among Us characters look like real astronauts.
Although, this one is kinda sus. Good, but sus.