....S.......W........N........E
..
.........................P......2♦(2)
...3♦(3).....P.....3♠.......P
...3NT....AP
(1) Either 11+ with a club suit, or any 17+
(2) Multi-2♦
(3) Strong cue bid (?)
The director was called, she explained all the options, 1♣ was not accepted, North passed and East opened with a multi-2♦. South talked to the TD about his options away from the table. She asked if he might have a comparable call to the 1♣ opener, and he said yes, 3♦ is a forcing cue-bid, equivalent to the strong part of the 1♣ opening. That's what offender chose, North alerted it and when asked said he didn't know what it meant. He did seem to be aware that it was artificial and forcing, so maybe it was all good. EW were not happy when 3NT-1 gave them a flat board.
What I thought was interesting was what happens if offender claims to have a comparable call, but partner reads it differently. I don't know of any defence to a multi-2♦ in which a 3♦ overcall is anything other than natural, but I suppose it's possible to have an agreement that all hands with diamonds start with a double, so 3♦ is a cue-bid. I think I'd expect to see this on their convention card. I don't know if the TD asked to see it.
Would you just accept whatever South tells you about replacement calls, and consider adjusting the score afterwards if doesn't turn out to be so?