IIRC, one reason his PhD was so hard is he spent a bunch of time working in a grind-it-out field (automated bug-finding) with an advisor who was sort of an outsider in the field. That's a recipe for a ton of hours spent on the wrong stuff with little agency. He only pivoted toward his current focus on HCI, learning, visualization, etc incidentally near the end of his PhD.

Since he's now familiar with and known in his chosen area, he may honestly be able to say to his students "I can help you do meaningful and rewarding research".

(Of course, I dunno what the actual story is.)