I don't think that anyone who is passionate about the mastiffs and having to work in rescues and shelters is ever okay with hearing an oops happened. There are some valid questions that are asked above that even if it is an oops litter are things you or your friend should be looking into and discussing what the outcome should be. Your boy not being interested before and making it to 4 years of age is not an indication that nothing would happen, it probably just means that the other females weren't in standing heat so he wasn't likely to waste his time.
Also liking the birth of puppies to children is apples to oranges, children are not euthanized daily due to over-population and this is something that touches a lot of people who have worked in rescue or shelters so you have to understand you touch a bit of a nerve with people when you sound excited or happy over your oops puppies.
It is also a good time to plead to others if you are planning to keep your animal intact (whether for breeding, or because you don't believe in spaying/neutering) ensure you know how the reproductive cycles of the canine work and keep your pet safe.
Also liking the birth of puppies to children is apples to oranges, children are not euthanized daily due to over-population and this is something that touches a lot of people who have worked in rescue or shelters so you have to understand you touch a bit of a nerve with people when you sound excited or happy over your oops puppies.
It is also a good time to plead to others if you are planning to keep your animal intact (whether for breeding, or because you don't believe in spaying/neutering) ensure you know how the reproductive cycles of the canine work and keep your pet safe.