I think people are still confused if he means splitting (ie, like you'd split a round with an axe, ie, facing the grain), or chopping through like you'd do to make a long piece of wood shorter.
And of course by "people" I mean "mostly myself".

So, splitting a round that is 5in in diameter with one swing should be fairly easy for most big knives, if the piece isn't too long. CHOPPING through a 5in diameter log in one swing is unlikely, unless you have the strength of Thor, or happen to call a lightsaber a "fixed blade".
If you can take repeated attempts /different methods then both things are easy. Batoning something that size is cake with the right knife, and chopping through something that size shouldn't take more than 2-3 minutes for most knives/people.
And of course by "people" I mean "mostly myself".
So, splitting a round that is 5in in diameter with one swing should be fairly easy for most big knives, if the piece isn't too long. CHOPPING through a 5in diameter log in one swing is unlikely, unless you have the strength of Thor, or happen to call a lightsaber a "fixed blade".
If you can take repeated attempts /different methods then both things are easy. Batoning something that size is cake with the right knife, and chopping through something that size shouldn't take more than 2-3 minutes for most knives/people.