It's implied, not stated.
In every instance where the book speaks of people being moved into an occupied space, the exact same thing always happens. The person moving into the space falls prone.
Due to that, it can easily be assumed that the rule applied for ALL situations. Simple logic. Just remember that it only applies when a person ends up in a space occupied by another, NOT when moving THROUGH a space. (In other words, any time you are FORCED into an occupied space or stop in an occupied space.)
In every instance where the book speaks of people being moved into an occupied space, the exact same thing always happens. The person moving into the space falls prone.
Due to that, it can easily be assumed that the rule applied for ALL situations. Simple logic. Just remember that it only applies when a person ends up in a space occupied by another, NOT when moving THROUGH a space. (In other words, any time you are FORCED into an occupied space or stop in an occupied space.)