You do realize there are three officials, it only takes one referee to watch the shot for a foul or travel or any other call. (By the way a travel would not have been the right call there even if he did walk a little) Anybody who knows basketball will agree that that the game clock determines the end of the game not the buzzer. In that situation with not much time and the gym being loud at least one referee has to have an eye on the clock.
I made those arguments only to express to you that the buzzer is not what is important. Where you’re really wrong is your quote "If the horn did sound at the proper time, then the shot is definitely off in time. (But again, I'm not sure that happened)" I am assuming your basing that off of the YouTube cell phone video which was taken in the middle of a loud Gallatin student section. I have watched the game film (recorded by an actual video camera set up on the second section away from most noise) and on that video there is no doubt the buzzer goes off before the shot. Pretty simple to me.