Ronnie is a beautiful cream semi-longhair non-pedigree. From the photo and from a postition of ignorance (not my breed) I'd say he looks a bit more like a Norway Forest Cat than a Maine Coon. However both those are natural breeds from similar climates (so is the Siberian) so yes, non-pedigree cats that look a bit (or sometimes a lot) like them keep cropping up.
He is a lovely cat.
He is a lovely cat.