I'd guess he's not indoctrinated by any terrorist group but was taking opportunistic revenge for the mass slaughter of civilians and the huge Russian participation in it.
The massacres and crimes committed by the Russians & Syrians almost make Isis look like humanitarians.
A couple of years ago, i watched actor Mandy Patinkin being interviewed about his role in the great tv series "Homeland". He mentioned learning a lot about world affairs while doing research for his role over the years. He learned that there's an extremely fine line between people we deem as being 'terrorists' and ourselves. He added that people we call 'terrorists' see us as being the real 'terrorists'. He added that if you look at the other side's point-of-view, it's very easy to see things like they do, and vice-versa.
I agree with Patinkin's statements. Look, we've been dropping bombs on people's heads in the middle east for over 20 years, probably more. Those bombs killed and injured hundreds of thousands of people. They completely destroyed families and ruined lives. They ruined villages, towns, cities and countries. And they're the terrorists???? Put yourself in their shoes and you just may conclude differently. Just imagine how you'd feel if you'd be having dinner with your loved ones and suddenly a foreign bomb just happens to be dropped on your home. Maybe it was a bomb that was meant for your neighbour's house, who knows. Maybe it was a stray bomb. And then you wake up in a hospital with an arm and a leg missing, and you're being told that your entire family was wiped out. How would you feel?? Would you feel like welcoming the country who bombed your home and killed everyone with open arms?? My guess is that you'd spend the rest of your life trying to retaliate and you no longer would care if you lived or not. You'd probably want to die for the cause.
That's why the difference between us and the other side is a very fine line.
