I can eliminate the idea that the two best OD guys are the outside, the two best ID are the inside and the last guy is the man to man guy.
(42762298)I don't have access to the PBP but looking at the advanced stats available from the USA offsite, it is obvious to me that Menard was selected to match up with Mayberry as the number of contested shots he was part of was too high to not be the case, plus his backup having a high number of contested shots as well solidifies that. Depending on GS at the time, Menard would have been the best or second best OD guy, though, so that kills the "leftover" theory. He does have better ID than the other top OD guy, but worse shotblocking, so unless there's a weird GS issue, it's fairly certain to not be just OD + SB.
This is definitely an interesting endeavor, though. It would be nice if there was something in the rules that gave some sort of indication how the "and one" was chosen, or if it was something we could set in the lineup, but that's an issue for another forum. ;)