I actually JUST emailed Wanda about this, I'll let you know what she says! (I applied both regular and special circumstances, but only because I'm 31, and I feel like that's reflected in my resume and PS and doesn't require any additional documentation haha)
It's not yield protection. McGill routinely has people with high stats accepted. Stop the fake news. McGill has all their admission criteria online. Numbers alone won't get a person in.
People apply to other schools. McGill doesn't give AF if you've applied elsewhere. It's normal to apply to multiple schools.