If this is a real threat then MuseScore really handled it the worst way possible and they should be ashamed for purposefully threatening to endanger a CCP citizen. If it's not, it's just a mafia-style shakedown.
Once again: if you don't see a problem with calling the CCP police on someone whose only personal information we know is that he's anti-CCP, then I don't think we have enough ethical common ground to even continue this discussion.
Edit: I agree with you that if this musescore developer is lying about that, then that would be wrong of them. But I don't think I have enough information to make that judgement. So I think that's where we're disconnected. At least for open source projects, my view is to take any and all potential legal threats seriously until the matter is resolved with the lawyers.