Yeah I suspect the traffic did drop when Yandex's spiders and all the colocated AI systems stopped crawling your site; data from cloudflare confirms this. It's not a coincidence; it's just not what people are claiming it is. You'd probably see a similar drop if someone bombed data centers in the US, but that doesn't mean they're running social media troll bots. AI bots are responsible for a lot of traffic these days.

Do you have any information on what user agent strings the suspicious traffic was using? Yandex bots might still use their user agent string even if they were crawling through a VPN. AI bots would probably masquerade as a standard browser, but would be likely try to crawl your entire site unlike natural traffic visiting a few pages. With VPNs in play it's too difficult to say for sure, though.