“Something is off”

Question

In this paragraph, does "something is off" mean "something is not right", "something is different" or something else?

There was definitely something off about Mr. Bittner today, she thought. It wasn’t just the way he paused at certain points in his lecture to look at her. Teachers were always doing that, the good ones, anyway—scanning their classrooms during their lectures. But every time Bittner paused—every time—his eyes stopped upon her.

Thanks!

Answer 1

Something unusual, not quite right. He was acting a bit unlike himself.