50 billion barrels of recoverable oil at $90 barrel is a gross of $4.5 trillion $ . Soros and his boys are involed and the big oil guys are salivating over 900,000 acres that PXD holes the rights too. There is some serious playing going on behind the closed doors!
Not only that, but he's forgetting transportation costs of that oil from the wellhead to the purchaser, so he can't assume the full $90/bbl. When inexperienced retail investors don't understand why a stock is going down, they tend to believe in conspiracy theories like "the stock is being played/manipulated."
Actually, in this case, it's probably just more sellers than buyers in advance of the preannouncement. Furthermore, there are many PXD holders who may have waited til 2013 was done to sell to avoid having to pay taxes until 2015 on their 100-200% gains.