That's not a great source. By "of its kind" they must mean accidental booster stage impacts. NASA intentionally crashed 5 different Saturn V 3rd stages into t

That's not a great source. By "of its kind" they must mean accidental booster stage impacts. NASA intentionally crashed 5 different Saturn V 3rd stages into the moon. At least some of those impacts were to generate vibrations for the seismometers they installed on the moon. See the Wikipedia article linked by the sibling post.