Hi there!
My name is Linda, and I'm a vet working on this site. I'm sorry to hear about this issue.
The concern here is that items like this can cause gut obstructions, particularly if the cat manages to swalllow strings or threads, which can cause the gut to 'telescope' in on itself. So we really want to stop this habit ASAP.
The first step I'd take is to have all of these items he has been chewing hidden where he cannot access them inside cupboards or closde laundry hampers. We should leave nothing out.
As the behaviour has improved significantly since being let out, it does sound like it was triggered by boredom, yes.
We'd hope and expect that he continues to do well, now he is out and about and getting some fresh air and exercise!
Our Bengal also chews, and is drawn to wool, plastic and pool noodles in particular. She has eaten large portions of her cat cave, left a giant hole in a fedora, and chews the pool noodles that I used to keep my boots in shape. The most recent thing was eating one of the "bird" toys. All the feathers and the plastic part that attaches the feathers to the string. The piece caused an obstruction in her intestine and she stopped eating, was nauseaus and dry heaving for about 24+ hours. After an x-ray we could see a foriegn object lodged in her small intestine. She had emergency surgery about two weeks ago and is recovering fast. But we had to buy a giant dog crate and make an appartment for her so she would just rest and not run or jump. She had a little onsie on - with a hole for her tail. (Total cost for this was about 3,500.) So, yes, keep an eye on these Bengals - they have to be engaged with and stimulated - or they will get frustrated and tear things up and eat them.
