If you read what he wrote, he explains the whole thing. While yes aerodynamics are going to be different on a gravel bike they are still important while racing at least to some degree and improving things even if slightly will be an advantage to those who haven't. The reason that Team Sky/Ineos whatever had such boring wins is the marginal gains, they do help even if boring or maybe a touch silly to some.

He explained the rando bag being faster then having a bunch of bike packing bags as it is an easy carry all with easy access rather than fiddling around with where you will put something during a control or stop. Plus at least according to him it might help a bit simply because it is blocking your pedaling so less turbulent air.