Couple ways you cool look at it. Either it is true or false.
My opinion is:
It's on Facebook so it must be true! I personally won't believe it until I get a re-tweet about it.
BMW has probably put enough 2013 M5s on dealers lots to carry themselves for 2 years pf M5 sales in the US. But logic hasn't stopped Marketing/Sales "geniuses" in the past from making odd decisions about product changes. If I was waiting for the LCI for my M5 purchase, I would definitely need something more significant than a dealer FB post to get excited.