Imagine a cube $100\times100\times100$, a million little cubes. We randomly pick half of them to be red, half to be blue. Define "connected" to mean, two red cubes sharing a face. (You could redo this allowing, just sharing an edge. or even, just sharing a corner.) So how many connected red sections would you expect on average?
I don't think we'd get just one. ~ $1/64$ of the red cubes should have all six neighbors being blue.
Sounds easily programmable in a specific case: start from the top, work down and sideways one cube at a time, make a running list of disconnected red sets. As you go, see if any of those sets just got linked - combine them. Keep going and combining sets and adding new ones till you get to the bottom.