I'm going to speculate and put forward reasons why this may have been a bomb. That the early reports of the pilot saying he had a technical problem and wanted to divert were all wrong, and generated from Egyptian sources. I do not say the early reports were deliberatley wrong, but it is in Egypt's benefit that it was a technical fault and not a bomb, so the early "mood music", which often sets the scene and is all many people ever bother with, is important. Egypt cannot let this be a bomb as it will make the tourist recovery even more difficult, and the industry has never fully recovered from the 1997 Luxor massacre due to periodic terrorist attacks over the years in Cairo, middle Egypt and of course major attack in Sharm el-Sheikh in 2005. This shows of course that there are terrorists who want to hurt Egypt. If it was a bomb then it will also hurt Egypt more if the aircraft comes down on Egyptian soil and not over the Med or any other area on the route to Peter. That Russia is now engaged in Syria must be seen as a possible cause for this being a terrorist attack, and of course more than ISIL will want to hurt Russia. So on one side there is sudden technical faliure, which is very rare to happen so quickly that pilots cannot send SOS, and on the other all the reasons I put forward for it being terrorism. To me the balance, without yet any forensic details known, tilts more to terrorism than accident. We should know by tomorrow morning I think.
On another matter, not all independant Russian airlines are "cowboy" operations. Orenair is an excellent airline, tho it is now Aeroflot owned for a couple of years.