I don't know how the interaction in question went, but it's possible they were just interpreting an earnestly concerned police officer as suspicious because of a (justifiable) distrust of police.
It's fascinating to read about inherent fear of being questioned. I don't think its ever crossed my mind, and its not uncommon to see cars parked along side random roads all through Oregon and Washington. I guess I'm lucky in this regard.
I wouldn't say the general population trust police officers. Being able to trust the police is a form of privilege that minorities, the poor, etc. often don't have. Most individuals from an upper-middle class background don't have reason to distrust the government.
The people on HN are probably an exception. I think perception of law enforcement depends largely on whether a person has found the authority figures in their life to be benevolent or malicious. Authority figures, especially law enforcement, tend to view those outside the norm with suspicion.