If you look at the reg above it says "flight time". Since he was deadheading home (he didn't fly after the deadhead) this is legal. He just has to be able to look back 24 hours from the end of his last flight he operated and find 8 hours of rest. Not from the end of the deadhead. There is no 16 hour duty rule, only uninterrupted rest required between flight segments. You could legally deadhead for days without ever getting a break and to the FAA they wouldn't give a crap.

Now, deadheading before flights does count because you are not "on rest".