That's ancient conjecture from when autos were first becoming popular. It's been disproven over and over by everyone who upcans from solo cups to bigger pots.
A previous member here built his own airpots that were about 2' tall and his autos flowered around the same time as the ones in his regular pots. The tall pots' roots never hit the bottom, so there goes the "resistance" theory!
Got cold enough to snow from the looks of it...noice!
What makes autos so variable from seed to seed is the need to breed in the correct amount of ruderalis to make it an autoflower but still have the THC everyone wants in their cannabis plants. That's how I can grow this:
and this:
from the same batch of auto seeds.
As to what sends them into flower, I'd say any type of stress. Mine never liked the variables that came from growing outside: hot days, chilly nights, and RH from 60 to 98%.