They had never seen anything like this before!
Not even William had ever seen such a thing!
If this had been in the past, William would have never been able to perform this kind of "imagination."
First of all, this wasn't his dream, he couldn't add a background setting to himself like a creator, saying that he "had finally reached a certain level after many days of hard practice," and then start off as the strongest.
Furthermore, the William of old fundamentally believed that a sudden expansion of spiritual power meant certain death or injury; these axioms restricted his imagination like shackles.
But now it was different, he truly believed in the "miracle" shown by Heine.
Hence, he could supplement the process in his mind—explaining the unknown with the unknowable, achieving a self-contained loop, which is the origin of faith.
William knew that these living people were conceived by his mother's imagination, so he didn't make things difficult for them.