Oo, I'm totally on the fence here. 
Dd2 is quite sensitive to noise and light, but only some noise and light, and from (randomly) a school experiment about tone, we know she has real issues with specific frequencies. So, sometimes, she can be oblivious to quite loud noise, but a slight change in frequency or something out of the blue (even after a period of the same loud noise) can trigger what looks like a Moro. (When she was younger the response looked like a drop seizure, now she can usually stay upright, but she has to grab something for support).
And, um, in those situations, I've probably been guilty of taking the 'easy' explanation for her behavior by gesturing to her wheelchair. So the wheelchair per se isn't the reason she has sensitivities to noise, but it's shorthand for 'issues' if you like.
I'm wondering if the lady was a bit embarrassed about having jumped so visibly, when most people would not have, and was a bit flustered, so explained the easiest way, with a 'signpost' of disability. I know I do it sometimes... And I wonder whether dd2 will use the same way out when she's an old duck in the supermarket.
It's just a way of coping, I think. She obviously wasn't embarrassed as a littlie (too busy screaming after hitting the deck when her legs collapsed), but even know I see her startle out of the blue (and we hang out with a lot of kids who have autism, so she's more than used to unpredictable loud noises) and then flush, as she knows it's not a normal response... so she's embarrassed about the startle, especially knowing that the other kids can't help the noise. She doesn't have to explain in this situation, as everyone knows she has a disability, but she's still embarrassed...
She could just have been a woman in a supermarket making a point about a loud kid, but I dunno.
The cafe woman is similar - I don't have claustrophobia, but have had a few occasions where I have absolutely lost it as I can't see an escape route (twice when sitting in the back of the car... A situation I have been in a gazillion times). But she might just have been an odd woman in a cafe. 
Folk are strange, no doubt.