Opposing calls

[Mike51]

NF I was the R in a junior varsity contest a few days ago. During the second period there was a pass attempt of about 25 yards down the sideline (Linesman side).
Obviously, I did not see what happened between the reciever and defender.
The pass was incomplete, but the was a flag thrown by the linesman. We met about half-way and he reported OPI and it was accepted and enforced. No big deal, no complaints from offense.
Fast forward to yesterday. I ran into the BJ from the game and as we talked about the game, he said he saw the interference, but thought it was clearly DPI. He stated he did not throw his flag b/c he saw the L toss his.
Now my question: what if they had both flagged the play and had different calls? how should this be handled?

thanks