If you can find out why 1 YC makes sense in the same scenario, I'll be more prepared to answer you.
For context, my role in this scenario was captain not ref, which is why I'd be ok with that outcome. My reasoning as a player would be that the ref must have a valid / logical reason and they are applying that reason equally in a scenario of equal fault.
As a ref, I wouldn't have given a YC at all, but I could see other refs trying to justify it was reckless from both players nonetheless, for their reasoning of a YC to each.