Your spot on jeeves.
This is exactly what happened.
I was airborne on the same frequency during the event.
Yes, the guys asked for priority from ATC 2 or 3 times using the term "unruly passenger" and yes ATC struggled with the concept. After these few attempts and ATC reading back "confirm sick passenger" the lads reverted to Mandarin to get themselves understod.
I never actually heard the term "hijack" used on that frequency however I beleive the boys set the applicable transponder code. Probably out of frustration. Anyhow... if you take the FOM at CAL at its literal best they had no problems justifying such a decision.
Seems like it was handled just fine in the end. Untill they got on the ground and the Taiwan media got involved that is!