"Fault" is not in question here either. Let's say I leave my front door unlocked. If you enter my home without my permission, you have trespassed and can be charged with a crime. The only thing I would be "at fault" for is making a lackluster attempt at securing my home. I don't forfeit protection from trespass under the law for that act though.
You see, locks are not what govern access; laws are. HTP is clearly in the wrong here. They forced entry in to Linode's systems, then attempted to extort Linode in an effort to achieve their goals. Swap out Linode's servers for Linode's offices, and there's no question that HTP are operating outside the boundaries of ethical behavior.