Well, that mentioned user has expressed genuine disapproval of your way of answering before. While he didn't provide any examples or explanations of what in particular he finds wrong with those answers (and without those I personally wouldn't subscribe to his assessment for now), it doesn't seem so much that he downvoted them because he doesn't like you, but because he just doesn't like those answers. And while an explanative comment for downvotes is encouraged, people are free to downvote answers they find bad.
I thus wouldn't call it serial downvoting yet, given that those are only 5 answers at the moment, stretched across 3 time periods, and with 3 of those 5 answers on currently active questions, and only 1 of those with a high number of countering upvotes (and thus objectively seen "pretty strong"). And that user already said himself that he looked at your other answers and found many of them inappropriate (even if not exactly saying in which way).
So while it stands to wait how this situation unfolds, I would not call this out as serial or abusive downvoting for now (be it only to calm down the situation). But I would strongly encourage that user to comment on the individual downvoted answers and explain what particular problems he sees with them in order to help improve the situation (if not done already).
(I don't want to say your complaints are completely ungrounded, but as a general advice in the spirit of mediation: As easy as it might seem to downvote in a personal and abusive way, as easy it is to take honest downvotes personal purely based on previous unfortunate encounters with the respective users.)