That's not really valid in the age of Swype-style keyboards. Less effort to do one swipe than multiple taps to hit individual letters for txt type.
Also, if you text and drive I sincerely hope you hit a tree or something else solid that doesn't hurt the road traffic and pedestrians around you - alleged FSD or no, we don't have level 5 fully-autonomous cars yet and so not paying attention to the road is just as bad as drunk or drug driving.
Or maybe they were texting and using FSD ;)