If you follow their youtube you will see their uh footage of downing.
Lots of speculation but one thing ISIS has never done in the past is lay claim on something they did not do.
This is a false claim by them. The altitude of the jet, the speed of the jet, heat-seeking missiles, RPG or small arms wouldn’t be able to reach the jet.
Nonsense claim.
(Of course, if they had radar guided SAMS, then they might be taken seriously. . .but in this case, it is a laughable claim.)