A lot of people are like that, they hardly start a conversation, not because they feel big, it is just in their nature not too. but when you get familiar with them, you get to know them better.

I for one know not to judge people by their first impression because first impressions are often deceiving, but it is a norm for people to judge you at the first few seconds the meet you, it is the way the brain tries to cut corners to know how to interact with others.