Does that mean that it was the right decision now?
No. You can't base the decision evaluation on future events / facts not known at the time.
Say you decided to randomly kill someone. Then it turns out that the someone you randomly killed was planning a massive terrorist attack.
Does that make your decision to randomly kill someone "right"?
No, of course it doesn't.
That is, of course, a crude and extreme example, simply serving to illustrate a point. In practice, there's a lot more gray. When analyzing a decision by a coach to not go for it, it is nearly impossible to factor in all of the elements that went into the decision.
Let's say you decide not to kick a 50-yard field goal, even though that would have even the score late in the game. Instead you go for it on 4th and 10.
On average, there is absolutely no question which is the better choice, but note that "on average" qualifier. We don't know the specifics. Maybe the kicker was throwing up on the sidelines from the strain, maybe he was injured, maybe the wind had picked up, etc. Some things we know about, some we think we might know, others we just don't know. And partly the decision also has to be a sort of "gut feeling", a concept that includes coaches taking into consideration all those things that aren't easy to label.
What we CAN analyze is a sufficiently large set of decisions. All those annoying unknowns tend to cancel each other out, letting us know if a coach (or group of coaches) is consistently doing something sub-optimal.
This type of analysis allows to quite easily see that NFL coaches are, overall, much too "conservative" and all too often play to "lose later" rather than maximize the overall chance of winning. Applying this to any single decision by a coach is not as easily done.
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