I agree, what I saw was him running his block, and then as he became a kind of last man standing, and as conservatives started clinging to him out of desperation, I think he decided to run with his new status, and see if he could actually become a real candidate.
Santorum was thrown out of office by a larger margin than O'Donnell lost, in her effort to win her first office. Santorum is looking for a way in politics to make his living, and out of work rinos looking for a niche in American media/politics, is always bad news for conservatives.