It didn't matter whether or not they did it to NATO, you are talking about Response vs Nuclear Response (AKA MAD), just because Russia didn't nuke NATO does not mean NATO will not response, because the next up if they (NATO) let it fly will be they are going to nuke NATO to see if NATO is going to response, which is something NATO cannot be allowed to happen to simple see if they are going to response, meaning they (Again, NATO) would have to nip it in the bud
As a former US Army Officer, and working under NATO command, if Russia uses nuke in non-NATO country, the STANDARD NATO response will be sending in NATO Peacekeeper all the way up to No Fly Zone impose on said Non-NATO country. That's the standard response, and if Nuke are used on NATO soil, the standard response is MAD.
Just because Russia nuke non-NATO and NATO would not use Nuke back in kind, does not mean they will sit on their arse and do nothing, the threat matrix has changed, and that would warrant a response. How hard is it for you to understand this?