I think we all stereotype people. It's just what the human mind does. It sorts things into categories and ascribes characteristics based on categories. The answer is (I hope) to be aware that this is a trap that we can fall into and try to keep our minds open. When you become aware, it's surprising how often we do it.

An example from just yesterday: I was driving away from work, and I noticed an older white man (late 60's?) walking his dog. He had a very upright bearing and what I could see of his hair was very short. He was wearing a jacket with a large American flag sewn across the back and a baseball cap made of some kind of camophlage material.

My first thought was, "I wouldn't want to be friends with that man." I judged him that swiftly. Then I started trying to unpack my assumptions and conclusions to see what they say about me and my mental processes.

Of course, clothing is a bit different from other more fixed things, but you should try it sometime. See if you don't put people into categories based on weight, age, gender, race, etc. It can be really subtle, and you may not notice you're doing it at first.

Having said that, I think your therapist's question was a dumb one, but we all say dumb things at times.