I think it's really all just one big shitpost, not much more to it than that. Though one addition, Shambler-chan being dressed up in a jacket and baseball cap is a reference to the "Timbler," a photoshopped image of a shambler in a jacket, a baseball cap, and wearing Timbs.

I'm not sure who first made the "Timbler" but it became a running gag among "boomer shooter" fans on twitter like Kinofabino, FPS Carol, and David Oshry (CEO on New Blood).