Implosion rather than explosion. The tin is buckled inward due to the vacuum seal rather than bulging outward from internal happenings (i.e., fermentation).What does that even mean!? I've only been smoking for a couple years, but can safely say nothing like that has ever happened to me. Of course, I've never tried Royal Yacht, so it may be this experience is unique to that blend?
The comment was also kind of implying that the Royal Yacht must be dead inside as it doesn't seem to be fermenting any or enough to bulge the can back outward. There are many factors involved though. C&D does leave some amount of air in their tins which likely not only aids in some fermentation, but already is taking up space which allows the tin to bulge faster as other gassed are created. The super vacuumed tins are much more air empty, so all of that space needs to be refilled first before it could bulge.