... here's another possible interpretation
Before and during the 4th down play, Romo knows that the entire game hinges on that last play. He tells himself "this is my last play." The play ends, he glances up at the clock, sees a second left, and (only) for a second thinks, "wait, there is still a second left." Then, just as quickly, he realizes that the extra second doesn't matter.
If he was convinced that he had another play coming, he'd have acted much more decisively and vocally, and someone would have had to tell him that he was wrong.
There is a decent chance that he was just temporarily confused when he saw a tiny bit of time left on the clock. He knew the last play was the last play, but for a split second thought he might just have another play when he noticed a second was still left on the game clock.
It could have been just a minor and momentary brain fart that most humans experience from time to time.