all of the same rules apply as Duty to Retreat. Outside of being expected to retreat if you can (and only if you can in complete safety). Reading the article, what it is really about is does someone who is prohibited from possessing a firearm allowed to defend themselves with a firearm. While self defense, anywhere, can not be claimed if you are engaged in criminal activity. In this case, carrying the gun is the only criminal act. It does not say what the previous conviction was of. For all we know it was for insider trading or pot possession 35 years ago.
Personally, this is where I agree with Canada's gun laws. Unless it was a violent crime, you may legally own a gun again once you do your time.