James Irwin and the Genesis Rock

ICR recently posted something about Apollo 15 young earth creationist astronaut, James Irwin.   They had a quote about something he said about the "Genesis Rock".

Most of the rocks previously brought back from the moon were dark, dense basalt. Scientists knew that if the moon were composed entirely of this dense rock, it could not possibly be in its present orbit. It would be too heavy. They knew there had to be an abundance of lighter material, lighter in density and color. Our mission was to find a lighter rock from the mountains on the moon. While we were exploring…[we] found…a pure, white rock, the oldest rock brought back from the moon—part of the deep internal material which had been ejected to make the mountains—and the most important scientific discovery of our mission. The press labeled it the “Genesis” rock, for it confirmed the fact that the earth and moon were created at the same time, giving scientific proof of the creation story of Genesis 1:14-18.

How did the Genesis rock confirm "the fact that the earth and moon were created at the same time, giving scientific proof of the creation story of Genesis 1:14-18"? As far as I can tell, they used dating methods that ICR finds inaccurate.