Not so sure. If the security at the event said "these people are active threats to security", then its the police's job to remove the threat and then investigate.

However it should now be on those lying about it that made the accusation to prevent their evidence, and if that's not good enough then to revoke their diplomatic credentials.

If the event was a private function as it appeared to be, then removing them is fine, but from the report it sounds like more accusations were made then "these people are no longer allowed at our event", and like the boy who cried wolf, that's where the problem needs to be sorted.