Check the description of the 4♥ bid and especially the number of hearts it promises for south. 4♠ down one when GIB is not able to count.
EDIT:
Something went wrong with the copy from the handviewer.
The bidding after 4♥ continued with North bidding 4♠ which went down one.
Keep in mind that BBO switches the players when GIB would be declarer. So North was GIB during bidding.
Correction of the Hand: