I had dinner with Mike Walker, who is on the jury (but not in this case, since he provided photographic evidence).

The basic scenario was this:
Wind about 6 kts, light current running upwind. Tom K. coming into the mark on stbd. Because of the current, it was easy to overstand. Tom was probably cracked off and footing to the mark.

Jason Hess and Bob M. were coming into the mark on port. Jason was to weather of Bob and overlapped from behind.

Jason tacked, and Bob tacked about a second later, well within the zone.

Tom had room to duck beneath them and still make the mark, so 18.3a didn't apply.

The jury found that Jason and Bob broke rule 13 (While Tacking) and tossed them both.