I don’t think it’s that unusual. ‘Indian summer’ has long been a thing. And I well remember one day over 20 years ago, out with dds on 31st October - temp was in the low 70s, so 20/21, gorgeous, warm sunny day.
The very next day, 1st November, was truly November-ish- much colder, wet and blowing a gale, autumn leaves whirling everywhere!