And it's related to how he deals with his own son of proximate age - to wit, he basically pretends he doesn't exist.
Trump doesn't know what Thunberg said; she speaks in long, complex sentences using long, complex arguments, and tbh even if he was in the room and actually trying to pay attention, it's so far away from the words-of-one-syllable-bullet-points-and-pictures style he's capable of assimilating these days, she might as well be speaking in ancient Greek.
But anyway, he heard that a yung peeple was speaking in front of the UN, and shat out a platitude about blah blah yung peeple blah blah positive blah blah teh fewtcha covfefe.
Yeah, this also is related to the obvious cognitive decline of someone who, once his dad was dead, had the whole world revolving around him his entire adult life.