Bacon is throwing up!! Aspen litter?

I recently decided to put in a litter box in Bacon's cage hoping that it would keep his cage cleaner.
I bought Aspen pellets since I read on the forum that Aspen is ok for hedgies
and the person at the petstore recommended it also.
The first day I put it in Bacon had lots of fun burrowing in it and totally terrorized his cage.lol
It also looked like he chewed on a lot of them.
I was worried that it might hurt his tummy, but he was fine for 2 days
and he stopped chewing on them.
However, last night I noticed he had a reduced appetite and didn't attack his kibbles like he usually does.
This morning when I checked on him I saw that he had thrown up about 4 times..
The throw up was a peachy yellowish color, not the color of his kibbles.
He barely ate his breakfast this morning..
Would chewing on aspen pellets cause this?
That's the only single thing that has changed..
Should I remove the pellets and switch to something else?
There's nothing in the pellets that would poison him, right?
The brand I bought is "Green Pet Aspen Supreme Pellets Pet & Bird All Natural Litter/Bedding"