You could have split the difference between getting involved and leaving to go into the store.
If you see something like this, take a moment, hang back and have a smoke or just play with your cell phone for a moment as you watch.
If its nothing, then no harm done other than you are late for the first quarter of the football game on TV, or at the worse, you enter the store after the time state law mandates no more beer to be sold (Its like that in New England...)
If the situation goes bad and you have to intervene, you have some more information as to what is going on, how many their are, and can position yourself to act in the way that keeps you the safest and achieves the result you want.
Let your plans be dark and impenetrable as night, and when you move, fall like a thunderbolt." (Sun Tzu)
In the aftermath, should their be one, you can better articulate your actions and observations simply because taking a moment to observe allows you to make those critical observations and decisions which will guide your actions.