I think it’s hard for the Apple corporate page to say that you must make an appointment in advance (and I suspect the original person was incorrect that you absolutely must do so or perhaps it is a policy for that store in particular), because that experience seems to vary a lot between stores. However, with the popularity of Apple products these days, it never hurts to make an appointment, and Apple’s support page should probably do a better job making that clear. I’ve learned that through less painful experience. We are only 15 minutes away from our favorite store, but after a few occasions where I showed up on the spur of the moment only to find no appointments available, I started making appointments as a matter of course.

It really does sound like there was a breakdown in communications with your first experience. They may well not have been able to fit you in (often they are booked solid and waiting around on the off chance someone doesn’t show up may be a waste of time), but they could have at least explained that in a more polite and informative manner. It’s good that you were able to find a more helpful store in the end.