We will know the "truth" after about a year. For now, I'm just as suspicious of 6.4 Ford claims as I was when the 6.0 Ford guys said they could run low 13's with nothing but tuning. Turned out, those who were, had more than met the eye. Typical "tuning only" 6.0's are 14 second trucks. Just like dyno sheets, time slips sell parts, so there is a lot of pressure inflate claims. Problem occurs when an innocent buys the parts and hype and doesn't get similiar results.
There are hundreds of "tuned" Dmaxes in the 12's. It's not even debatable that a tuned Dmax is potentially a 12 second runner. But if somebody posted they ran 11's with just tuning, I would be sceptical as well.