I never saw it on there. Have a MM:SS for it?
Around 20:44 when he equips the frost rune you can see for a second the number of potions he has under Long Bow (I think there are other places where he shows the favourites menu and you can see them, but I've found this one now), which is 15
Around 34:44 when he re-equips the dragon breath, right after he jumps down the tower and heals, you can see the number of potions he has are now only 11.
And there's a 1 next to the potions too, so it is marked to a quick-slot or something...
Don't know if we have the same video as mine is a bit glitchy...