N/S are decent players, and their team had won the league about 3 years ago, while E/W tend to occupy the lower half of the ranking table.
E/W play 5 card majors, 1♣ only 2 cards in case of 4=4=3=2.
2♣ was immediately asked about, and explained by North: "We play 2-suiter cue bids if only one suit was bid by opps. However, I do not remember if we discussed this case. I tend to assume that 2♣ is natural here."
I was called after the hand had been finished. The E/W bids were interpreted differently by the players. West thought:
the double showed ♣
3♣ showed ♣
3♦ showed ♦
East thought:
the double showed the majors
3♣ asked for a stopper in ♣
3♦ showed no ♣ stopper and minimum
Question 1: Assuming that North made the best explanation he was able to give, should this be presumed Mistaken Explanation as defined in Law 21B1b?
Question 2: If your answer to question 1 was "yes", should an adjusted score be awarded, and what score should that be?
Additional information, not really relevant for the case: Result as played was E3♦-1. The score at the other table of this match was E3nt+1. All 8 other tables reached 3nt, twice played by West with an overtrick. When played by East, it went down at 3 tables after a ♥ lead and scored 2 or 3 overtricks at the other 3 tables.