Flares are bright, bottle rockets too whimpy - don't have the fuel or the speed to chase a plane even at low-altitude immediatly after take off.
The bigger question is does anyone believe a SAM would miss at that distance?
I'm suspecting some home made device.
Sure, if the proximity fuse crapped out, or the warhead failed to detonate. The older SAM's are really only good in a tail chase, because they require the engine heat as something to home in on. They can fail to quite correct enough to actually hit that engine, but they have proximity fuses so that if they merely get close, their warhead is supposed to detonate. The description almost sounds like whatever it was passed ahead of the aircraft, which might mean it was fired too soon to "see" the hot engine exhaust and never locked on.
Far more likely to miss than not, given the probable scenario. And even if it hit, it is pretty unlikely to take down a plane that large.
The ever common SA-7 has a difficult time hitting anything but air when staring into the ass-end of a military jet. For shooting a commercial passenger aircraft, a crusty old SA-7 comes pretty damn close to being effectively unguided. It was a pretty poor MANPADS even in its day. Fortunately, it is by far the most common portable SAM one has any chance of being able to buy off the back of a truck. Most advanced MANPADS have a short shelf due to the use of cryogenics in the system design -- it requires factory service to replace the cryogenic component after several years in storage.