Interesting. Never heard of that rule.Very true.
One note, Jake Walman a couple years ago is an interesting case that might apply here I think.
Walman is Canadian born and raised, but had dual citizenship, Canadian and American. He attended a U20 camp for the USA, but was ruled ineligible by IIHF due to not playing in the USA for two full years. He was in his second year. Rochette is in his first in Canada.
Not sure if there's any reason it would be different for Rochette, since he is Swiss born and raised.
IIRC he already spent some time in Canada as a boy playing hockey, when his father temporarily returned to Quebec for work. So that might frees him from this rule.
As he hardly will make Canada's U-18 team this year, it's not relevant anyway.