That's a good point. I'm fairly certain that lady has said that to me before touching the food. I think some legally blind people are good with shapes and big contrasts. She may also be relying on smell and not expressing it.

If they have any sight at all, their ability to cope with that limited sight would also be greatly increased; that is, if their resolution is significantly lower, their relative contrast may be much higher, even if what the object is is much less clear, without context.