Never underestimate the ferocity of the beast that lurks just beneath the thin veneer of "civilization."
Warriors throughout history have found that battle and the horrors of war changed them. Taking scalps, fingers, noses, ears, and other grisly trophies was commonplace.
When society breaks down and we begin to revert to our baser natures, I wouldn't be surprised if we see these "gruesome" practices return.
Yeah. Even Sledgehammer wasn't immun to that stuff. Or he was tempted anyway.
But, definitely weird stuff tonight. I bet if you dig into it though, it was probably done for intimidation of other enemies or to provide entertainment and an outlet to the crowds or something like that. Just dressed up in "religious" things like becomming gods.