I agree the "question" is a stupid one...but it was a writing prompt. It was not a slanted question like those you suggested. He could have been creative and made up a story about anything....like saying he ran outside to see her on the end of a rope, attached to a blimp. That's not making fun of her, it's using your imagination.
It was wrong of them to punish him and suspend him.
It was also wrong for his mom to let him get away with this, she should have just said "Son, make something up".
From the letter sent to the mother, she told him to make something up. That was part of the evidence used against him. The more pressure put on him, the story he made up in his mind probably got less & less "acceptable" to any adult who would read it.