airliners are gigantic and SAMs aren't intended to blow up the plane, they're intended to detonate near it and shred it with shrapnel, destabilize it, and send it to the ground. this is perfectly in line with that.
and the whole "ukraine military shot this down" line has been pumped from RT and pravda all day. the leader of the separatists, strelkov, has already admitted to shooting down the plane and then attempting to cover it all up by scrubbing his and the separatists social media profiles.