I'm not going to argue that as it's always easy to blame dead people, but there's two different types of jamming.

One is to actually jam the signal IOW preventing reception. The other is to overpower the satellites' signals and replace them with your own. That defeats the doppler calculations of GPS needed for triangulation, and instead the receiver believes it's where the jammer wants it to be.

If the latter includes altitude information, then it's a huge problem.