Strange.
Spoofing the signal of a single GPS satellite would just result in the RAIM system discarding that satellite data.
And spoofing the signal of all satellites that are in line of sight would be extraordinarily complex, would be valid for a single airplane and would require knowing the exact location of that plane.
The only spoofing strategy that (I think) appears to be simpler is spoofing the EGNOS signal for en-route augmentation.
However, I guess that all GPS receivers can be set to enable/disable SBAS signals.