With a cat, you should make effort to eddy out or hold position, at least a bit of an effort. Once you've made your effort, they should clear for you. Yeah, cat frames can cause injury. If he doesn't then get out of the way, 'd have yelled at him GET THE FUCK OUT OF MY WAY, I'M COMING IN FOR A SURF.
If they don't move, you have a responsibility to not hit someone on the river if you can avoid it. Even if they are a dick and wrong. As others said, you don't really know what is going on with them and they could be seriously hurt or killed (unlikely but wouldn't that suck?)
I am a river, babe - I've got plenty of time, I don't know where I'm going, I'm just following the lines..... - "We are water" by Shaye