“Trained on a system” doesn’t imply current possession of said devices. I imagine that there are plenty of ex-USAF people alive who were trained how to employ a nuclear weapon, yet no longer have access to said weapons.

This being said, even if the missile did come from Russia and shoot down a plane across the border, it still didn’t make it a good idea for a civilian airliner to be in the same airspace a few days later!!! If you’re hit by a missile fired by the Russian military vs one fired by terrorists, you’re just as dead.

And the Russians have a long history of shooting first and not apologizing later.