It would have been so much easier for the pilot to say, "thank you for your concern. I'll check it out, and don't worry we won't depart with an unsafe aircraft". It would have cost 8 seconds of his time and satisfied the passenger. This is not an issue about whether or not non professionals can assess what is and what isn't a potential safety problem. It's an issue about good
PR with the customer. What disturbs me the most these days is how quickly ground and air crew resort to "I'll call security" even when challenged in a respectful and civil way. Had that experience myself a few years ago.