Why even bother? AMD isn't in such a position that such jokes can be made. If anything, this sort of thing just makes AMD look bad. They haven't even beaten Pascal yet (since we know jack-all about Vega's performance), they shouldn't even be looking at Volta. Are they trying to bait Nvidia or something?
The joke goes two-fold too, since he mentions more voltage for overclocking. AMD's cards have been terrible overclockers recently, heck people couldn't even really overclock the Fury GPUs. Is he trying to suggest that Vega will be very overclockable? Is that the hidden nugget? But it would be nice if it beats Pascal for overclocking purposes. They could get around temperature/efficiency issues that way. Clock/volt it low for better efficiency and if people want, they can throw heat and efficiency away for better clocks. Again, AMD shouldn't be (promising) joking about such things and getting people's hopes if they can't deliver.
An awful lot of pressure is on AMD already for what they will reveal at the end of this month, Raja has now just added onto that pile.