Sometimes nervous passengers see something they don't like the look of and come up with some utter garbage when they relay their concerns to crew.
As could be said of any of us in circumstances outside our competence.
Surely the main aim should be to encourage the cabin folk to pass on the concern, have it evaluated and then, most importantly, provide feedback to the passengers to allay the fears. Consider that, if one passenger saw whatever, others did also .. a PA is probably the best way to put it to bed.
I am reminded of an example years ago on a flight to a holiday destination. The majority of the passengers were first timers (this via cabin crew feedback along the way). At destination, the weather was probably going to require a diversion from the minima. As the workload during the latter part of cruise was low, I made a descriptive PA, including what would happen during a missed approach and what the folk would hear, etc. As it turned out we got in OK but there was a fair bit of positive feedback via the cabin crew in respect of passenger calmed nerves.