What evidence is that?
I've never seen a chain fire in person and had read years ago that they ran across the front and were prevented by using flammable grease. I'm not sure I understand how that can be. The shaving and compression of the ball when loading must make an airtight seal and the grease seems to burn off or blow off during the firing of the first chamber or two, so can't be providing much protection for the others.
Not sure that open caps cause them either but if sparks from one open cap did ignite a neighboring open cap that cap could obviously shower sparks through the nipple to ignite the charge. Of course that wouldn't happen if the pinched caps fell off at recoil like mine usually did.