I'm struggling with lalimes Martin's take there, the turnover had nothing to do with physicality or lack there of, Brannstrom just played it really poorly.
Puck hung up on the boards on him, he left space between the boards allowing the F1 to get inside position on him, he actually recovered well, winning the puck battle with the F1 and chipping it behind the net before F2 arrived, but he put it too far for Guinette to get who had coasted in ostensibly to provide support. Because Guinette wasn't there to provide the outlet option for Brannstrom, the puck went to the far side where F3 collected the puck.
But let's blame it on on Brannstrom being too small...