I love Cowboy but his low kicks always look weird to me...maybe it's the bent leg thing but not sure.
If you watch this vid above and the one Frode posted, it doesn't look his training partner is doing the same thing if that's what you are referring to (bringing the leg back bent to get back into guard quicker). I've seen some Thais do what I think you're talking about to get back into stance quicker, instead of bringing the leg back in a long arc.
Always wondered if Cerrone's bent leg on the low kicks was a flexibility issue but it doesn't seem like it since is body kicks look more normal.