“They would undoubtedly have to dump significant fuel before landing.”
The article says they were almost at the halfway point so that is not necessarily so. Also going back to the USA (west) generally you have headwind instead of tailwind.
Maybe they wanted to go back to US legal jurisdiction to deal with the disruptive passenger, even if near the halfway point.
So they dumped the excess fuel through the engines; it still cost a lot of money to bring the "disruptive passenger" back.
Good point about US jurisdiction.
I do wish I'd read a couple sentences further into the article before I typed my comment.