Below here, below this discussion, which occurred back in Nov of 2019, there are other discussions about the down vote, and which also include comments about the red flag, I think, and other comments.
A down vote happens, just as an up vote happens, and they happens and generally speaking, without knowing the mind of the giver, the best guess is that it is a statement of their mood at the moment.
They are not required to account for their vote, up or down. The computer system does know and does keep track and you can look at your G2G profile and see the evidence. You can see anyone's G2G profile and how many up votes they bestowed and how many down votes.
In general, I think the general agreement is that it is the problem that the one who bestowed it has, and not your problem