I agree with the comment in the article that it appears they were playing with it for at least an hour. It seems they fatigued it enough that they could take turns chasing it so maybe they had little breaks?
Off topic but while searching YOUTUBE for killer whales I came across this lovely little clip of an encounter with a sperm whale set to lovely music.
I didn’t “like” the way the whale kept opening his mouth when near humans but I see that one of the comments thought the whale was smiling!
http://www.youtube.com/watch?v=f7-y8LC50r8