I have reservation about terrorism being a cause, with the Uighur terrorists in mind. People travel on stolen passports for reasons other than terrorism. If the terrorists target a foreign airline, they will harm may innocent victims who are far removed from their cause and will only draw worldwide condemnation of them but sympathy and support for China. All that they have been protesting about would be undone by this act.
Instead, terrorists would hijack and make demands before doing anything drastic if they are aboard a foreign plane as opposed to a local one. And so far, no one has claimed responsibility. If there was an explosion, we should see some floating debris as Steelbird pointed out. It might still be early to spot them, so let's see in the next few days.
Passenger jets do go down seemingly suddenly without communication -- with technical problems.