If you had come in with the guy you'd have a RIGHT to speak.
If you worked for the store you'd have a RIGHT to speak.
IF you were asked by ANY of the involved parties for an opinion you'd have a RIGHT to speak.

As it was, you were merely butting in. Unless you overheard something unsafe being said, IMO it was time to be quiet.

You could always talk to the guy AFTER he left the store or stopped talking to store people.