Clearly what's happening is that EM travels through some medium we never accounted for even in a vacuum (what's a real vacuum in this universe anyway?). Neutrinos are so weakly interacting that they can completely ignore all everything and go at c. It's not that c is wrong but rather that we've been wrongly measuring it by measuring photons in a pseudo-vacuum. Whereas neutrinos are so largely unaffected by things that they come much closer to the actual value of c, because vacuum-spacuum you can send them through the Earth and they'd never hit a damned thing. My guess is that our typical measurements of the speed of light do not take into account the index of refraction of spacetime due to zero point energy. Which would be experienced by photons but not by neutrinos.
That or they're just wrong.
But, heck any medium does slow down light and less interacting bits of even the EM spectrum get slowed down at different rates. This is dispersion and it's the reason we get rainbows. Because different parts of white light are slowed down by different amounts. So in air you will find that radio waves can travel faster than the speed of light in air. Really a few scientists managed to stop light completely, and before that slow it down to a crawl. Heck, I can run faster than light in such cases. But, I certainly don't run at c.