A very unprofessional mistake at that level. Hmmm, do you blame the coach for the lack of coached drilling or the swimmer[s]?
US Track and Field has a long history of this sort of nonsense.
From France 24
The Americans touched first in three minutes 30.06 seconds before the stadium announcer said they had been disqualified "for an early exchange". France clocked a time of 3:31.51 to take gold, with Australia winning silver in 3:31.64 and Japan bronze in 3:32.26.
The Americans were denied what would have been a 12th triumph in the event in 15 championships since the inaugural edition in Belgrade in 1973.