I think you may be right about the call being upheld.
We've seen plenty of other instances where BB has not bothered to challenge a play if there is not good enough evidence, and I really don't see this being any different.
However, in this particular scenario I believe he should have taken a chance. It was only the first challenge, and he would've had one more just in case. It could've been the deciding point of the game, or at least one of the bigger plays anyway.
If it would've been the 2nd challenge, then I could understand him not wanting to take the chance. Since the implications of the game were very important, I think that he could've taken a chance.
I agree the timeout has value, but at that point is could have been given up without much worry.
I think it's just as much about timeouts with Bill as it is with losing the 3rd challenge, probably more. His thinking is that the potential of a lost timeout could have come back to haunt them late in the 4th quarter, needing to stop the clock. That is certainly understandable thinking, so I won't pretend to second guess him.