I don't think so, the images were pretty low res iirc. I did some googling though, and the only thing I found was somebody that said "the game reads the model data out from the file's alpha channel". However, I'd expect the data to just be appended to the end of the file, since PNG works anyway with that.

PNG is extensible, so they could totally have defined a PNG "chunk" in the private namespace and shoved the data in that. They didn't though. They treated PNG as just a way to store image data and wrote their extra data into the image, encrypted in an amateurish way.