It could have been a coincidence. A Russian airbus with 224 people – mainly tourists – flying from Sharm el-Sheikh, Egypt to St. Petersburg, Russia could simply have come apart in midair, killing all aboard. It would have been one heck of a coincidence, though, considering the players who would have wanted it to disintegrate and the constellation of agendas that would be advanced by a well-placed bomb.
It is almost impossible that the plane was hit from the ground. It was flying too high for a shoulder-fired missile. Although it isn’t clear whether there are mobile missile launchers in Sinai, assume for a moment that one or more exist. The missile would have to have been programmed – it needs radar and target designation – and therefore it needs a) to know the flight path of a particular plane if it plans to hit a particular plane and b) an operator with the right skills. (The list of requirements for a successful takedown of an airliner is what leads some to believe that it was a Russian operator in Ukraine who fired on Malaysian Air Flight 17 a year ago.)
A bomb inside the plane, however, would account for the widespread wreckage.