You seem to insist on the idea of the professional human being, but were you ever caught off guard at home, where you did not think about being professional? What if you then see 2 people walk up to you and talk to you like you were the suspect of an investigation? I personally would go into full-on “keep my family safe” mode which might or might not entail the call to the police. If it would not, then I might, depending on my inherent personality, talk to them to keep my loved ones out of this. The invasion of your personal space is something people react completely individually to.
The home is the place where people are the most vulnerable, at least if they grew up in the more safer part of the globe, where the actual danger of being attacked at home is pretty low.
Edit: My personal experience is that I somehow can keep my cool in situations like this and more often than not, answering questions leads to the more civil outcomes. That it wasn’t right in SupMatto’s situation isn’t really what matters, it’s the internal process in SupMatto’s psyche and how the PI’s affected that and how they tried to.
Edit 2: Also, I can’t blame PI’s for trying to get answers out of a suspect, it’s part of their job and so is to try and keep themselves inside the personal space of their suspect to subtly weaken their condition. It’s often a part of investigative work to walk across the lines of legality.
Edit 3: Clarification, grammar and spelling.