This USAF aircraft in international airspace was almost certainly indirectly involved in an ongoing military conflict. It's not there for no reason. It's very likely providing intelligence to the Ukrainian military, which will cause deaths in the Russian military.

I'm not saying whether that's good or bad, just that we should not be surprised they are expressing their displeasure with us being there. They avoided using missiles for diplomatic reasons, but given that this is clearly an aircraft aiding a combatant in a war, it's understandable that they could just shoot it down. The only reason they are not is because they're being cautious about expanding the war, but we're already provoking an expansion of the war by using our aircraft in this way.