No, absolutely not "obviously". It's not a criminal offence in the UK to film people without their knowledge. It breaks data protection law (civil); there are regulations (RIPA) for public authorities but these do not apply to members of the public ; and there is criminal law that covers covert recording if done for sexual gratification, but those may not apply if the cameras have not been placed in toilets or bedrooms.

Can you link any of these laws please? Especially for Ireland. I can't find anything for Ireland that would make this a criminal offence.

Again, I'm not defending it. I think it's an awful thing to do. But "why didn't they call the police?" is answered by "maybe they did and the police told them it's not a police matter".

Unethical, immoral, obviously. Criminal? Not at all. Starting with different laws in different jurisdictions, over the difference of criminal acts and civil offenses to the point where an AirBnB is your private home and not a hotel ("obviously" you're allowed to film your own home right?).

If it's criminal or not is not a matter of simple opinion, but of the laws in that jurisdiction. DanBC doesn't deserve the downvotes.