No, reality.
Everybody can get stronger. Just a matter of it being feasible. Given that none of us really know Cain's exact training program or how his training cycles are laid out, we cannot really comment on how this would be done.
However, everybody can get stronger. The best strength athletes in the world manage this every year (to a point, of course, eventually it comes to an end) so people with far less strength can get stronger much easier, as they are less close to their genetic limit.
Given that increases in strength can come from areas other than increases in physical mass, and many of these areas transfer far better to peak power output for a fighter, well, it follows that it not only can be done, but might be a priority for some athletes.
Given that lifting to increase strength really does not take that much time in comparison to the volume of his other training, a few strength based cycles should integrate nearly seamlessly with the rest of his training, and might actually improve certain aspects of it (such as injury prevention/reduction, which should be a cornerstone of a decent S&C program).
This is rather like asking if athletes who compete in the decathlon can get stronger. Of course they can, and their training volume is often best described as insane. Does not always mean that it is what is necessary or optimal, but increases in strength rarely hinder an athlete.