M&S have always (in the last few years at least) been open about who makes their wine, with the producer in small print. I guess in this case they just decided to make the producer more obvious - either because they thought it would sell better or as a result of negotiations with Musar. Presumably Levantine is a brand made only for M&S?
I disagree a little with M1tch. I quite like the earlier-drinking Musar wines. They do IMO let you know what to expect in the Chateau wine - in terms of flavour profile and VA - even if they do not have the same weight. But don’t buy them just to save a few pounds - if you want Chateau Musar then you need to buy it.