Those questions are very rude. Rhetorical questions are fine, rude ones are not.

How do you deal with them? Do you have a prepared answer to shut down the conversation?

If someone asked why I was short (I am, but no one asks) I would probably say "I'm genetically meant to be this way". For the others "I am quiet because I only speak when I have something to say" and "I walk this way because it's my biomechanics". Perhaps these people are just not very clever and need things explaining simply to them.