I don't know how he reached that conclusion. So he's getting more data than he used to: with that, you can figure out the average age of people responding to your surveys, now. You can't compare that to past data if you didn't collect data in the past, so you can't conclude 'younger.' You can certainly conclude it anecdotally, and, compared to the 90s when CCGs and LARPs were sucking away the new generation of potential RPG fans, it certainly seems plausible. Likewise, "selling great, but we won't share any numbers," is what WotC has said every time.
I guess, as someone who works with data, I'm just suspicious of those kinds vague claims and conclusions. But, in spite of there being nothing new to the marketing speak, I really do get the impression that D&D has recovered from the Great Recession and the rift of the edition war. For one thing there isn't this cloud of negativity surrounding it, it's own fans are no longer actively trying to wreck it, instead there's a relatively united front of support for the game (Pathfinder notwithstanding). That was a major 5e goal, and it looks to have been successful. The point about using the right technology this time around instead of heavily investing in the wrong technology is also a cogent one, for instance. It's not just picking the right horse this time, it's not betting more than you can afford to lose. WotC has just had a much less risky, more realistic, business plan for D&D this time around, and it's paying off, even if it does mean a slightly lower profile at GenCon.