how so?
Russia literally said as much, no assumptions required
the coup happened, Russia took Crimea, action and reaction, doesn't mean it is justified, it was obviously the trigger and later officially confirmed by Russia as it felt the situation had deteriorated to the point where they had to protect Russian people in Crimea
just like the Ukraine NATO flirtation went on for years while being protested, a red line was drawn and crossed, then war happened, you can argue how justified that was, you cannot argue it wasn't the trigger