I always thought it's merely a difference between AmE and BrE, then I stumbled upon this post by Gordon Ramsay (about vegetable choice for a small garden):
Parsnips are amazing through autumn and fall. Not just roasted, but in incredible soups.
I googled the difference and besides BrE and AmE, I only found Canadians treat 'Autumn' as more formal, but with the same meaning.
Is there something I'm missing? Say, 'fall' being 'late autumn' or something?