Personally, I think much of that art looked quite interesting and not without merit.
The idea of Ronald McDonald at the last supper with dollar signs above is a sophisticated metaphor, I'd be interested in seeing that work in more detail (Edit: I see it's not original, though, but still it speaks to the mindset). It's not necessarily un-christian, it could actually be an interpreted as a commentary lamenting what has become of christianity, i.e. that society worships commercialism now.
The busts with horns and torn up bibles, though, are more of a blunt instrument. I'm guessing the purpose was exactly to inspire the kind of outrage that they indeed elicited in the man who made the video. In that sense, they are clearly successful.
Trying to put myself in the shoes of the creator(s) of that art, I get the sense that it stems from a deep cynicism of christianity and possibly the frustration a highly creative mind would have growing up in the kind of stifling religious environment that it seems might be present in the broader community around that school.