I think you don't want to be THAT ref that sent two guys from the same team off at once. I feel for Barnes as I think he probably knew 17 deserved to go off as well, but did not want the backlash. He's already endured a bit in his career.
Still, 17 should probably have gotten a yellow at least.
EDIT: Maybe he could have yellow carded both and made a recommendation for the citing commissioner, although I think that is at this stage strictly limited to the opposing team, but I am not sure. The ref should be able to say: "Hey, you're at fault, I'm going to submit a report for the both of ye and have the board decide your ultimate penalty after the match, for now you both get yellow"