While in it’s regular state sisal should be okay, but being that it was made to be a durable rug, they may have created it in such a way that it’s too tough. (and too much at one time) Yes, some vegetable fibers can be too tough. Just an example — celery should be cut down to to little pieces as the fibers in celery can cause issues if there is too much. Not that a rug would be made out of celery fibers, but that is just an example of just because it’s natural doesn’t mean it’s safe.
I have a bunny that is a big rug or blanket chewer. (Thankfully we do have hardwood floors most everywhere and she seems to avoid rugs and blankets that have our scent on it) But in her space, we placed industrial floor carpet tiles that she has unsuccessfully been able to really get at, but I also distract her with sea grass mats that she can chew up to hearts content. She shreds those and consumes the mats made for bunnies, (in BinkyBunny Store).