This has come up in the past, but in regards to Samsung (allegedly) paying Verizon employees more to sell their device.
If anyone, including older relatives you cite, wants an iPhone specifically, wouldn't they go in and ask for one? Certainly they will need assistance to check out due to how buying a carrier-tied phone process works. At no point, at all, did they say "am I buying an iPhone?" If the phone itself they thought was an iPhone, then maybe when the sales rep brought the box out and it said "Samsung Galaxy S6" they didn't think "maybe this isn't the phone I thought it was?"
If all of these scenarios did not prompt them to ask if what they were buying was an iPhone, then really, did they want an iPhone? (Or is iPhone just synonymous with a certain segment of the population to mean smartphone?)
We were at the AT&T store for a billing issue, they weren't looking to upgrade at that moment. So they were just looking around while we waited 2 hours for our turn. They held the S6 and thought it was the same one they've seen on the Apple commercials on TV.