Well, if they practice a system then they are part of that system. Does it seem not logical?
But many historians consider Jats to be outside the caste system. This idea is also acceptable as Jats are considered to have come from outside India and hence they were foreigners. Why do they follow the caste system then? Or else, who amongst them follows the caste system? History sources show sakas and Kushanas to be the followers of prevalent religious practices of their time i.e., Buddhism, Hinduism. In my opinion, Hinduism and brahminism are not one and the same thing. The caste system is part of brahminical belief system, but not per se of Hinduism, I think.