No, I don't think it's "normal" to be angry at someone else trying to make small talk. Annoyed, maybe, but as long as you keep your annoyance hidden, it's probably with the realm of normality to think to yourself, "Why do you give a crap if I've (a. lost weight, b. been up to anything, c. been living on the streets)?".

Some people with PTSD seem to be quick to anger. Someone told me that angry people usually feel they've been dealt a raw deal in life. They're angry at the injustice of life. I honestly haven't got it all (or most of it) figured out yet.