Some people derive quite a bit of pleasure from buying "the best". They simply aren't interested in hearing that what they are doing is wrong. Or ways to save money.
The key here is:
"Instead, this guy asked me why I needed the i7 processor and 512GB SSD. "
That's not really his business to stick his nose and interrogate you (like a parent would) to try to prove your thinking wrong (not saying that some people wouldn't like this or be appreciative of course). On the surface seems like a great loyalty builder. But maybe not.
Take the lady that wants a fur coat. You're going to tell her she's stupid and should want a good cloth coat?
Take a guy that wants a fancy watch or a fancy car. In their mind there is value that extend way beyond the real benefit of the device. A guy wakes up and wants the Porsche Turbo. He doesn't want to hear that at 160k he is wasting his money. Now if he asks your opinion that's another thing of course.
There is no question that with some buyers you will gain good will by following the path described in the story. But please don't assume that everyone wants this, appreciates this, or that it is some just so above it all business ethics that everyone should emulate.
By the way having an external drive has advantages and disadvantages. (Personally I would never travel with my photo collection but on the other hand having it on a drive means you have to also protect the drive which becomes easier to steal or lose.
[1] We don't even know how important the money savings were to the buyer in this case. Perhaps he had millions I would guess that the store salesman had no clue to his financial condition at all when deciding he shouldn't "waste" his money.