You said: "Chris Heisey continues to hit better against RHP than LHP." As I understand the word "continues" it means ongoing. Through today.
The last time Chris Heisey hit better against RHP was 2011. This is unassailable.
Your sample size argument is also incorrect. Heisey hasn't just hit LHP better over a "small sample" relative to his period hitting better v. RHP.
Heisey's 2012-13 period, in which he's hit better v. LHP, encompasses 454 PAs. The earlier period you rely on, 2010-11, Heisey's "RHP" period, encompassed 534 PAs. The two periods are roughly equal in sample size, separated only by 80 PAs.
Heisey makes my point exactly. He's a perfect example of a player who initially showed a reverse trend in hitting same handed pitching. Then, as time went on, he reverted to the norm.
I won't predict his future trend, but I would reject any idea that he is currently "better against RHP."