I like to imagine that some developer commented out that line to allow for spying on Canadian persons and left a "TODO: find better way to identify US numbers" that was never fixed.
That’s hilarious, although I suspect “don’t hack the US” means “don’t hack five eyes” in practice
While it would be funny, Canadian phone numbers are pretty easy to identify, generally. They have their own set of area codes. Granted, there are exceptions, though I guess it depends on your interpretation of what it means to be a "US phone number".