Mental Floss took a look at the flammability of Doritos a few years ago during their first test of internet “life hacks”. They burned a lot better than expected.
If you want to see a Dorito fire out of control, it’s at about the 9:40 mark in this video:
Doritos have different spices and such than regular tortilla chips, but I would expect regular tortilla chips to be just as combustible.
Rags soaked with oil or other chemicals like paint thinner can spontaneously combust (see bump’s link). I agree that it’s probably something similar with tortillas.