Yeah I’m guessing this is a false positive based on heuristic analysis, i.e. the TOR program has a lot of the same behaviors as malicious programs. Of course it is more accurate to say that the malicious programs are copying TOR behavior or just straight using TOR code, whatever the case may be.
My main issue is that it kind of shows a lack of due diligence. I assume the official TOR binaries are signed, so the official TOR binaries should be exempted from these heuristic positives. If the binaries are unsigned/have no valid certificates, then I can totally understand the false positive. At that point, the user should know they are installing software that cannot be automatically verified as being safe, and antivirus should never assume that something is safe otherwise. Like you said, for typical users this should be the expected behavior. Users can always undo Windows Defender actions and add exemptions.