"Anyway if we're talking a singular event/audio recording the KT red album has to be it right? "

It depends on how the question is asked and how you are defining "influential".   Did the Kingston Trio influence the majority of PROFESSIONAL musicians who cropped up durnig the folk revival? The answer is probably "no". Did their music influence the majority of TRADITIONAL enthusiasts during the folk revival? The is very likely "no".   Did the Kingston Trio influence the largerst MASS AUDIENCE during the folk revival? The answer is most likely "yes".   

I don't think we would have had a "folk revival" or a "folk scare" if it wasn't for the Kingston Trio.   Folk music would have existed in some form, as it still does today, but it would not have gone in the direction that it did.   When the Kingston Trio burst on the scene you suddenly had record labels throwing money at musicians. Clubs and coffeehouses sprang up to support the growing scene.

Let me use another analogy. You can't grow a single tomato plant and say you have a garden. (I guess I am getting hungry - pizza and tomato in two analogies!) You can start a garden because you enjoy tomatoes, but you will probably realize that you can grow peppers, oregano, basil, lettuce and suddenly you will find your plate is full - and you are enjoying everything that you grow.

Influence is a tricky word. You could probably argue the same about rock music. Most people will cite the Beatles or Elvis Presley, but there are many different "influences" for both fans and musicians.