I'll note, Samsung's "PR numbers" for 10nm density were slightly lower/worse vs later shipping silicon - Qualcomm exceeded Samsung's 10nm density claims by ~10% (of course, the usual debate of "what is transistor density and how to measure transistor density" rages on). Again, I see no reason to disbelieve Samsung's claims for their 8nm processes, a derivative of their 10nm process.
Even if Nvidia only managed to match Qualcomm's Snapdragon 845 (a 10nm product)'s transistor density, that would still be 56.4MT/mm^2, far better than the "50%" claim. Again, this is against both shipping products in the real world and TSMC's own claims for their 7nm HPC process (claimed at 66.7 MT/mm^2, FWIW).