It's been years, so I can't recall exactly, but when I was doing all my initial research on how to raise chicks, I came across a lot of users advising that it's a must to brood them indoors for the first few weeks.
Maybe (and hopefully) more people have caught on by now that it's not true. I remember seeing a lot of posts over the years of people asking if their chicks would survive being moved outdoors at 4/5 weeks, etc, in very decent weather.
And maybe the info I got wasn't from this site. It could easily have been elsewhere.