You’ll never know who did the voting. There are some odd people who will just downvote any comment. There are also people who makes bots to do the same. Every chance that some idiot didn’t like that you have an opinion, but it may not be that at all.
When you input your password, then your biometrics (faceID, fingerprint, etc) become active. A restart requires you to enter that again. The police can make you put your finger on your phone or look at it, but they can’t make you divulge your password without a court order.