What we know is that two apparent passengers were on board with stolen or forged passports. Obviously they meant mischief, since you don't travel internationally on a stolen passport if everything is above board.

But when you think about it the sorts of mischief that could be involved are quite many and varied. One can't rule out terrorism, but it's one possibility among sufficiently many that this is not where I personally would start. Far more likely you are dealing with organized criminals doing more typical organized criminal things (like smuggling stuff).

Additionally usually if the plane is intentionally downed, someone will want to take credit/responsibility. That this hasn't happened is an indication, particularly absent patterns of attacks here in the past, that this is just criminal business as usual and not related to the accident.

Finally there are early unconfirmed reports that the Vietnamese navy may have spotted smoke columns yesterday. if that turns out to be the case, it would be a strong indication that the plane exploded on impact with the water, not in the air.

At present I am so far from being able to endorse the T-word explanation that it doesn't seem worth looking further into at this point.