A key point may be that one opponent trashed a Copper, and since Curses were already gone, the game automatically made them gain a Copper as replacement, without any user interaction. idaho7777 probably expected to click 3 times for his 3 opponents during the Swindler effect, but Swindler was over after 2 clicks and the third click was not giving out a Swindler to his opponent, but buying one for themselves.