The tweet offers no context as to whether October will be the reveal month or the ship-to-customers month (it may be both), but an iPhone 12 delay makes sense.
It's likely more than just a supply chain issue: many Apple Stores remain closed due to the Covid-19 pandemic, and, importantly, given the economic uncertainty, people may not want to rush out and upgrade to expensive new iPhones in September.
Is this a credible iPhone 12 leak?
Apple doesn't officially comment on its planned launch events until about two weeks beforehand. So we may not know if the September 8 date is null and void until the end of this month, and the October date may not be revealed until mid-September.
Prosser has been responsible for some bold, inevitably proven accurate leaks – new MacBook Pro 13-inch and iPhone SE 2020 timings were right – but his WWDC 2020 predictions were off: iOS 14 wasn't called iPhoneOS and AirPower isn't coming back.
The iPhone 12 launch event – which will almost certainly be digital and not in person – seems to be a moving target at this point, one that's situated between two months, with the latter timeframe becoming more believable by the day.