Since archive.is doesn’t scan the internet and only archives content on demand, those might as well have been planted exactly for this purpose - which would put another crime onto the accuser.

A false flag ploy is a massive accusation that requires strong evidence. I agree this organization seems suspicious but I wouldn't hint at accusing them of intentionally uploading child sexual abuse material somewhere and archiving it with archive.is without a smoking gun.

I don't know why they first went to the host and not the entity itself but positive evidence is important. A false flag report wouldn't shock me (I've seen it happen many times) but I'll withhold judgment until further investigation.