Here's the problem, Andy.
That BU did give up the call by not making one. He shouted across the field that he did not see a tag. That means the PU who may not be in a position to help, must make the call or, by default, the runner is safe. God help.....no, even God isn't going to be able to help an umpire who openly asks for help, doesn't get any and calls the runner out. Sort of like pointing to a players glove, "show me the ball", the player opens the glove and shows it and then the umpire calling the runner safe!
My tenet has become "make the call what your eyes thought they saw." Apparently, the BU saw something to make him think there was a tag and then doubted his eyes. Unless completely taken out of the play, I will always make the call.
I do not care what a coach/player/fan thinks, if there is a possibility that I missed something, I'll go for help if requested. If you have coaches who believe that is a license to make such a request on any play and you allow it to happen, that's the umpire's fault. If there is no doubt you were in the best position and saw all the elements, just say no. And, more often than not, I've had a coach/player thank the crew for getting together even if they didn't get the call being sought.