The way you typically sit is probably not consciously chosen. You sit the way you've always sat. It is subconscious and natural. Linguistics stands for your language. In this case, your non verbal language.
Programming is just like a computer program.
It is a program you put into place to achieve a specific result. Mirroring, which is one of several NLP techniques, is the art of copying another person's behavior to create a relaxed communication situation. The reason being is that we like people who are like us. They will like us at a subconscious level. They are just like me.