I was putting them up in good faith as a public service.

Yes, they did. But when I pointed out that they didn't in fact own the copyright they highlighted this detail about the youtube terms if service, so I still had to take the video down, not because it violated copyright, but because it violated the YouTube terms of service.

Youtube enforces its own terms of service, not them. They just bullied you into removing the content so they can keep their ad revenue from the views without having to compete with you.

Sounds about right. They flagged it via the youtube process so I don't even know how I would dispute that with them.

Which part of the Youtube terms of service did it violate?

I dont know, here is their contact info:

https://stock.periscopefilm.com/contact-stock/

As I said, super unpleasant folks.