100% spot on. So really, it's not just a micro-fissure. The solder actually wicks itself out of place, creating an air gap. What really causes this, other than "thermal cycling causing solder pump", is totally unknown. You shouldn't be able to "reflow" a CPU...
You do also need to keep in mind that these guys are likely using some weird blend of metals that is highly un-tested except in-house. There's probably some dude whose job it is requires him or her to play with this stuff day in and day out, until he retires. I'd love to talk to this guy.