To a point. His is a generalisation and in this situation context is everything. I do know that the NATO Secretary General has made it specifically clear it will not act against Russia over Ukraine because of the fear of war in Europe, nuclear or otherwise. That Russia has nuclear weapons obviously changes the dynamic if they are used, but let's be clear, in these other circumstances the threat of all-out continental war was not a possible outcome, which also defines what action NATO might or might not take.
The statement that NATO's past actions are defined by whether or not the opposing state was a nuclear power is glib and doesn't sufficiently contextualise the individual circumstances.
It's not a conclusion that can be applied in this circumstance simply because it isn't the sole driving factor behind NATO's stance. That Russia has nuclear weapons obviously influences the situation because nuclear weapons are held in a different context to conventional weapons but it isn't the only consideration.
Diplomacy is a treading fine line and acting on behalf of other people's interests comes loaded with conditions.