[stouset]

I don't think circumstances around your anecdote leave room for it to be factual. "Red delicious" isn't simply a breed of apple — they're all trademarked clones. The offspring of an apple tree won't produce anything like the fruit of the original apple. In fact, the overwhelming majority will be inedible and only suitable for cider. Genetic drift isn't really plausible because there's no mechanism by which these trees would drift genetically.

New apple strains are, as far as I know, not really bred for. They're found in the wild.

I may be wrong, but I'm pretty confident that an apple that isn't a strict clone of red delicious can't be marketed as a red delicious. It's also possible that growing conditions now have changed enough to alter the fruit, but I'm not positive that it would be a large enough difference to notice.