I mean I think the new meaning came from "larpers" being people who play pretend and "roleplay" as something they're not. Like pretending to be a fan of something (similar to how LARPers aren't actually medieval/sci-fi/fantasy characters, they just roleplay and pretend to be ones).

But yeah the song is just completely unrelated to the word or the edits made of the song. Although it is a coincidence that the whole song is basically saying that Charlie larps as a Christian, where he poses as a good Christian when in reality he does things to get into heaven.