Everyone has their own opinion. CSS has it's own syntax, and is interpreted by a web browser to style a web page. Next you'll say interpreted languages aren't programming.
I would like to point out web sites are web applications, therefore fall into this category. The fact you had to put the person down by saying "CSS isn't programming" only shows you're here to try to make yourself look better than everyone else. Everyone on this forum are too quick to find an opportunity that makes themselves look better than everyone else, stroking their egos.