Words can have multiple meanings, my friend.

The word's root just means "full of mystery", which is completely appropriate in this context -- describing people who accept the authority of fancy equations as a mystery, instead of delving deeper for a justification from first principles.

It's true that mysticism also has a more specific meaning i.e. describing particular strains of religious or philosophic thought and practice that are tied to the idea of "mystery" in a different way, but I see no reason this meaning should have a monopoly on the word, considering the etymology, see https://www.etymonline.com/word/mystic?ref=etymonline_crossr...