To clarify further, the part you're referencing is this bit (I assume as it's the only part related to the topic):
The reason there is no source cited and it says "is likely to have" is because the author wishes to make it clear it's merely his opinion. Short of the US declassifying it's intel there's no way we can know if any of this is correct, but it's irrelevant as it doesn't actually support your claim anyway. It says the missile was Russian made not that it was fired by Russia (which is technically incorrect too as the author is using Russian made as a drop in replacement for Soviet made, and that's not how it works).
So while your conspiracy of Russia shooting it down is quite enticing, as you have nothing to support it but your gut I will opt to stick with the known facts/official story. That it was Ukraine pro-Russian rebels who shot it down and that Russia helped them make the evidence disappear.
Sorry, you're wrong