everyone. I was curious about this tradition and looked into it and its history. There is no definitive event marking the first round bought by a player acing a hole but may assume it was the result of exuberant golfers celebrating their accomplishment with others and eventually became customary to buy a round for everyone.
In my experience different variations of this tradition have taken place. I’m certain people have just left and not come in the clubhouse but I had someone buy rounds for everyone and someone buy just for the group. The chances of an ace are about 1,250 to 1 for an average golfer so these accomplishments should be celebrated.