mmm. NATO responded more out of a sense of gratitude towards the US for the resources it had poured into the alliance, as well as in realization that it was the first time anyone had ever activated the "musketeer oath". If it didn't respond the one time it was actually needed, that might pose some serious questions as to its future usefulness.
But, it's actually pretty dubious whether there was any threat to US territory. Which was always the situation imagined.
It was a case of "close enough". I suppose. Article 5 is the fire alarm, you can't have it not work, it has to work.