AvE, while funny, is actually a really good teacher. I found his Toutube Channel while I was going through my electronics engineering degree.
He explains **** like your 5 and uses universal language pretty much everyone can understand. He's awesome. Total zombie/SHTF type guy you'd want on your team!
He's wrong that the barrel length is the primary factor contributing to increased accuracy for most people shooting carbines vs pistols.
It's ergonomics (more points of contact with the firearm) and/or increased sight radius, and/or optics that make it easier for most people to hit with a carbine. But, it's not primarily barrel length. It only takes a couple/few inches of barrel to fully stabilize a bullet. A goof like that makes me doubt everything he says.