You may not have stated the words “You’re wrong,” but that was clearly what you meant by this response to me saying it is still hay.
For clarification, there’s no such thing as “long stem fiber.” It’s long stem forage.
Fiber is a chemical with a specifical chemical makeup (well, there’s multiple types of fibers so, fibers are chemicals with specific chemical makeups). There are long-chain fibers and short-chain fibers, but these are referring to the chemical structure and are not changed by a physical alteration like chewing or cutting. Similar to how cutting a brick of butter into a small piece for your potato. It’s still butter, it’s just a smaller piece. So chewing forage still leaves the same forage, just in smaller pieces, same as chopping up and pressing into a block or pellet. Starting with a long stem doesn’t have any chemical difference than the resulting short stem of the same material. I have been unable to find any literature with a reason for needing long-stem forage other than the chew-time consideration for digestion in grazing animals. I see no chemical reason why the same chemical would be processed differently in the digestive tract. Other than that a too-large length of hay that doesn’t get chewed up enough may not have enough time to digest fully, so you might see more pieces of intact hay in their poo.