Sam in the wheelchair

Yesterday in the car while I was driving the kids to school, Mia started telling me how everyone in her class but her was teasing a boy in a wheelchair. She kept telling me how she was the only one who was nice to him and the other kids were mean to him. It was breaking my heart. I asked Mia if he was new to her school since I don't recall seeing a boy in a wheelchair at her school.
Mia: No.
Me: Is this something that just happened or has he always in a wheelchair?
Mia: He's always been in a wheelchair, his name is Sam.
Me: How do they tease him? What do they say?
Mia: They make fun of him because he can't run.
Me: Well, it's nice that you're his friend it must really hurt his feelings that the others are mean to him.
Mia: Yeah, I'm the only one that gets to push him too. Not fast though. The other kids tried to push him fast and made him fall out of his chair but I don't go fast...unless he wants me to for fun.
When we have gym with Mr D. in the gym he has to stay with Mrs. Thornhill because he can't run.
When we dropped Mason off at school we included Ms Elizabeth (Mason's teacher) in our conversation.
Miss E: That's not good that the other kids are not nice to him. Maybe you need to tell your teacher.
Mia: I told Mrs. Thornhill but she didn't believe me.
Miss E.: Sometimes you need to tell adults more than one time....
Mia: I did that already but she didn't believe me.

Miss Elizabeth and I both talked some more with Mia about how to be nice to Sam and to tell an adult that the other kids aren't being nice. It just really bugged me all day especially as I visualized some poor boy falling out of a wheelchair so I asked Mrs. Thornhill about it when I picked Mia up from school.
Mrs. Thornhill: We have a Sam but he's fine. He's not in a wheelchair. I'd just say Mia has a very creative imagination.

Creative or Scary? Should I be worried that she fantasized Sam was in a wheelchair?

Today when I picked her up she was telling me about Josh (a boy in her class) kissing her in the coatroom. Vhat? Not only do I have to worry about boys and girls starting to like each other but now I don't know when a story is totally made up. I suspect it is.....but is it?