I don't buy that hog. The metal around the void would contract away from the center point of the cold effectively making it larger.
A simple test would be easy. Take a piece of mild steel and drill a shallow hole in it say 3/32 of an inch.
Measure the hole with a caliper.
Then throw it in the freezer for a day and measure again.
Then allow the piece to come back to room temp. Measure it again as a control, then throw it in a 300few deg. Oven for a couple of hours and then measure the pore again.
"The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza
Baby Jesus cries when the fat redneck doesn't have military-grade firepower.