That’s not entirely true Bunny House. Maybe you’re thinking of bunnies without wintercoats? In that case you are totally correct.
Rabbits can tolerate the cold pretty well as long as there are places to hide from rain/snow/wind, they get something like straw to build cosy nests, have buddies to cuddle up to and are well prepared by getting a winter coat. Sudden temperature differences are very bad for bunnies and keeping bunnies with winter coats inside for a prolonged time causes them to loose the winter coat and they will get cold when they go outside again. Switching a bun from inside to outside should be done between the end of spring and start of autumn to make sure they will build a good coat. A quick Googling around tells me they can tolerate up to -20 degrees Celcius, but I would stick to -10 to be safe. My buns were completely fine between -10 and 30 degrees Celcius when they were outside. Just make sure to check the water often because it may freeze solid.
If your area gets colder than -10 and even -20 degrees Celcius frequently then yes I agree with Bunny House, it may be too cold for them but I’m not experienced with anything colder than -10 myself.