Was it glued to the pockets aswell as the foam border surrounding them? That’s usually the case. But maybe it wasn’t. Hybrids might have a bit different design. Its possible in your case they it wasn’t and that should be fine then. My mattress had a thin fabric covering the entire surface of the mattress and was simply glued to the edge rails surrounding it. It is noticeably diffferent if i remove it and lay directly over the coils.
The fabric was glued to the pockets as well as the foam border. Actually much more securely to the pockets than the foam. The “fuzzy” looking material in the attachment photo is a small amount of poly foam that stuck to the fabric when the foam was peeled off.
You were probably smart to leave that alone. I believe its for anti cupping and weight distribution.