Take a listen again. She said 30% were Trail Boss and an additional 30% were Z71, totalling 60% of Silverado 1500 sales being off-road capable (which really means having an off-road package). She specifically called out that 60% of sales were off-road packages
And yes, younger and new buyers are a thing to attract, especially when so many truck configurations are so bloody expensive, the high level trims have been priced out of the new buyer market. GM wants folks buying their first new car to buy high-margin vehicles like a Silverado, not a sub-$20k Cruze.
They need <35 year olds buying in if they want to keep selling the high-end trucks to older buyers, as the guys buying those high-end trucks are rarely buying their first truck. I expect the Custom Trail Boss in particular has sold well to younger buyers.