It's not as if we are ever going to learn the truth in these kinds of "incidents". Russia will say they were in Syria, Turkey will say they were in Turkey.
However this time since the pilot parachuted in Syria, and got captured by rebels, I tend to believe the Russian story. If the plane was shot down in Turkey, the Turkish army would have recovered the pilot, isn't it?
Jets move fast, wind blows a parachute around. It's possible that when the missile was launched, the Russian jet was in Turkey but by the time of impact, missile and jet were over Syria. Based on the description, it sounds like the Russians were flying parallel tot he border and flew across a small finger of Turkish land that protruded into Syria. It sounds like both countries are somewhat it the wrong. The Russians technically entered Turkish airspace, but they were transiting, not flying a sortie in Turkey. The Turks over reacted.