I presume SOP is to scramble at the slightest sniff of suspision of anything untoward.
If a hijack event a la 9/11 takes place, then their ROE would quickly be changed from 'intercept, identify, report' to 'clear engage'.
However, they won't know until they actually intercept the target.
In this particular event, little was achieved from a military point of view, apart from a usefull exercise and good
PR. Thankfully.