This is not a case of "ignorance is no excuse" but one of "forgive them, for they know not what they do".
I'd be curious as to how many things the OP is ignorant or uneducated on. While everybody is good at something, there's no one good at everything(well....except for some folks on gun forums).
As for the statement...
I'm glad he handed the weapon back instead of making a purchase.
I have to ask why? Do you automatically think the guy was gonna buy a box of ammo and start shooting, right there in the store? Maybe, he was aware of his ignorance and was going to ask about training right after he got his answer to the CWC question. We as gun folks, should be happy to see non-gun folks interested in getting involved in the shooting sports. We should not chastise and belittle those folks and their lack of knowledge, but be thoughtful and helpful, doing it with courtesy and respect. Over the years, I've seen way too many folks wanting to get into a new endeavor, only to be driven away by fatheads ridiculing them instead of guiding them.
I always get amazed at how upset folks get when being swept by a gun, they know is obviously empty and safe, while standing at a crowded gun counter. I help teach gun safety classes and I find it difficult at best to do it myself without taking the muzzle off the ceiling or the floor.......and I constantly preach muzzle control. I hesitate to even think about the amount of times I'm swept by empty guns at the Clays course or shooting range.
The guy was obviously new to the sport and obviously looking for help. There was a chance to be a mentor and a positive memory, if one presented themselves in the proper manner. Unfortunately in scenarios such as in the OP, way too many times chest pounding, inflated egos and impatience get in the way. Just like in the OP, folks many times are quicker to try and impress others as to their superior knowledge, than take the time to sincerely help.