Except it wasn't just a notification that there's been a complaint. It was "no more unwanted messages, please."
Aside from that it could be somewhat reasonable if there really is sufficient evidence to suggest that a criminal complaint is warranted. That seems unlikely, but I suppose we should keep an open mind. In the absence of someone digging up some really damning stuff from social media it looks a whole lot more like a lawyerly — and presumably therefore less illegal — attempt at something like "swatting", albeit a less violent version. The police should know better than to let themselves be used like that, but a lifetime of experience leads me to suspect that maybe they do not.
What was the problem again?