The Dutch term for Indian Summer is "Old wives summer". Referring to old wives knitting clothes at that time of the year in preparation for winter, in correlation to another phenomenon in late summer: an explosion of spiders making cobwebs.

Ableist, sexist, biologal-essentialism, so many red flags. Wait, red is a cultural appropriation as its differently used in different cultures.

Anyway, Indian Summer referring to people being late is completely made-up.