If it is a wind up, the purpose it would serve would be to give the OP the support she was seeking to tell the child's parents that what they are doing is wrong. Without knowing exactly why (and even if) they are doing what is reported, I'm not willing to condemn the parents. In short, strange though the behaviour seems, I can think of perfectly ordinary circumstances where a child needed to be contained for its own safety. I can even quote a couple of examples from my own family.
One morning, when DD1 was four and DD3 was two, I woke up to a quiet house. No children's voices. No sounds of playing. Eerie. I got up and checked their bedroom. No kids. Checked the rest of the flat. No kids. (We lived in an upstairs flat but had a garden beyond the garden of the downstairs flat — very Scottish arrangement). Looked out of their bedroom window and there they were, starkers, in the garden in the early morning, daubing themselves with mud and having a whale of a time! When the relief had washed through me and I'd smiled, I called them in. Hosed them down a bit at the back door and put them in the bath. It was a cold morning in May (Edinburgh still gets frosts into May some years). I can't remember what I said to them about going outside without telling me, but it didn't happen again. It scared me that they could get up and out without my hearing a sound, especially as my bedroom door, always open, was right beside the first exit door.
What if they had been devious and it kept happening?
A couple of years later, when DD2 was four, I discovered chocolate biscuit wrappers under her bed and chocolate smears under the pillow. It turned out she had been getting up in the night, going downstairs (we'd moved to a standard semi by then), moving a chair from the dining room to the kitchen, and climbing up onto a kitchen worktop to reach the top shelf of the cupboard where I kept the choc biscs, then putting the chair back again. Again, the scary thing was that she had done this several times without my hearing a thing! Anything could have happened!!!!!!! I promised DD that she could have a chocolate biscuit every day if she would promise me not to go climbing about in the kitchen (or anywhere else) in the night. It worked. What if it hadn't worked? What if she had done more dangerous things or if her actions had threatened a sibling's safety? (Playing with fire?).
I can imagine circumstances where a child did not respond to parental reason and explanations and kept on "disturbing their peace" or that of their other children so that they felt forced to take drastic measures, at least for a while.