Yes a lot of skepticism on that understanding. I don’t believe in magic numbers for much of anything to do with chickens, including how much room they need. We are each so unique in so many ways that no one magic number can cover all of us. If you want details on that follow the link in my signature.
Considering you are in Ontario and the weather that means, you will probably be OK with that size flock provided you don’t keep the second rooster, don’t have a broody hen raise chicks with the flock, and don’t integrate new chickens in the future. I’d feel a lot better if I knew the run was set up so they can use it in your winter. You might even be able to get away with some extra but the tighter you shoehorn them in there the more your odds of bad things happening go up.