I'm thinking it's easy to say that because what else can it be. But upmix from stereo does it give you true 5.1 because I'm experiencing true 5.1 in the song echoes. Anyways who ever did this up did a amazing job..
If it's the entire album, it's an upmix. Otherwise it might be the Pompeii soundtrack. Either way, it is not an actual surround mix of the Meddle album.
That doesn't mean it's bad. Some upmixes sound very good...as do some DPLIIx on-the-fly upmixes.