Yeah, I suppose the Spoiler Code is overkill, but why stop now?
Yes, you're right, that was the explanation. I just found it very
convenient that the Monster, who was last seen plunging through a flaming dock, somehow managed to find his way to the same underground room that Larry was in (more or less) and remained submerged underwater long enough to become dormant and remain there for forty years until a jackhammer "dislodged" him so that he was able to bob to the surface and be exposed to radio waves (nice touch there) and be revived at the exact same time that Larry was. Talk about a coincidence!