It is possible he was clicking quickly and did not realize he had friended you both when he clicked on the other guy. This has happened to me on a few occasions, Usually, if I am friends with both managers, i will not support either side (just to be fair). However, on a few occasions i see only one side and am in the process of clicking when I realize I am also friends with the other guy. Then I feel bad. There is no way to take it back and I would understand if the other manager got pissed about it. I’d love to be able to undo the support or send an “oops” message but such is life.