weird eating habits?

[Roachella]

I have a rescue pig who arrived with a tunnel to hide in. I don't know what this tunnel is made of, but it's some sort of woven.
It seemed to be a bit frayed when he arrived - thought nothing of it.
But it seems he is chewing it - it's getting more and more raggedy.
I don't, of course, know if he's swallowing it, but am I doing something wrong?
I give him the recommended food, and loads of interesting veg.
Please, is this to be expected?

Is the tunnel made of woven straw-type-stuff or twigs, like a doormat or a laundry basket? Or could it be compressed grass? These are designed for small animals to nibble on - it's good for their teeth and tummies. Even if made of something else I'm sure it would be safe for a nibble.
Make sure you give your GP plenty of fresh hay to nibble daily as well as other nibble toys like sticks and wooden toys. Hay is an essential part of a rabbit's diet (more important than pellets), and I think also for piggies?