I really think the way the Bears performed in those short yardage situations the rest of the game played into that decision. And the way the Bears responded in OT validated the decision. They did everything right up until the Interception and the game was theirs to win.
And one other thing to consider, something small but not completely negligible... By kicking the extra point, they ensured the Rams would play it conservative and take a knee, guaranteeing the game would go to OT. But I believe there were like 18 seconds left on the clock at the time and the Rams still had their timeouts. If you go for 2, and even if you make it, the Rams are still a few medium gains or 1 long play away from a possible field goal attempt to win the game.