I dunno, I think it is possible. I mean, if the roo made the first spurring count so to speak, and the cat was already weak from hunger (which would maybe make it go for the hen? I don't know, I am just throwing out ideas) I guess it is possible. I'll agree with those who have said they have never seen a cat go after a full grown hen. Me either. But I think it is possible. If the cat were starving or sick maybe. I wasn't there so I can't speak to the validity, but I think it's possible.
What i do know is that any cat that has come near my hens is chased off by my cochin, min'es a big girl, standard sized though. And the cats in my neighborhood learn pretty quick that a smarter course of action is to wait for the hens to chase after a mouse and join in on that chaos and maybe catch the mouse themselves than to try to go up against Matilda. (if by any chance the dog hasn't chased the cat off in the first place)
I think in my own convoluded way what I am saying is that I have never experienced a roo killing a cat, but it is possible. I am going to give the poster the benefit of the doubt because I have seen stranger things I suppose. And Roos are often protective of their girls. That quality among others are what has some people keeping them in the first place. Not all, but some.
So if indeed the poster watched his roo get the cat (bad for the cat, but good for the roo and his hen) then kudos to the roo. If it's an April Fools joke, then the "yolk" is on me because I fell for it. Either way, I'm cool with it.