That was what I initially expected when Shane showed back up at the farm without Otis, and would've felt more or less in line with what little we knew about the television version of the character. But, yeah, it was definitely a more dramatically interesting decision to have him betrayed by Shane.
I guess that's what we were supposed to think from Shane's explanation when he got back (although I couldn't make out half of what he was saying). Plus I thought it was a little odd that they didn't show what happened. Seemed like one of those "fast-forward to end" dramatic shortcuts they kept using on SGU.
I figured that what we were seeing was Shane skirting the dark side, getting over his problems with Rick's family by proving he was still willing to go through hell for them (and presumably coming out a better man). Although that hair-cutting sequence at the beginning seemed awfully dark and moody for such a conclusion.
Instead, we see Shane's trip to hell luring
him into the dark side, into which he will probably continue to descend-- and the hair sequence suddenly fits a lot better.
Too bad, though.