Derek Carr practiced today.

And Tua wasn’t concussed that time either. You ever been tested for a concussion. It’s not very scientific. Not saying he wasn’t or was but being in the concussion protocol isn’t the end all be all of it.
It's one thing to have a doctor mis-evaluate you. It's another to say Carr was faking an injury. For that to be true, Carr would need to influence the league doctor's decision. Very unlikely claim.