Thin Floor, Wasn't It??
When the being crashed through the floor to get the old lady, did you notice the floor was actually paneling with a hardwood floor pattern? Very thin stuff. Those of you who don't do home repair should know that floor you saw being broken through was the same stuff used on walls. A toddler couldn't have walked on that floor, assuming it was a floor. The old lady could probably have broken through that floor as easily as the creature did.
A standard floor constructed of 3/4 or 1 in. plywood is somewhat thicker and much stronger.