Villager Discount Is more than original price?

For context, this is a cured zombie villager.

After trading pumpkins, the trade went up from 1 pumpkin for 1 emerald to 3 pumpkins for 1 emerald. After trading again, the price went up again, but this time it was more than the standard 6. I have never hit this villager, and all of his other trades have remained at the reduced price.  Furthermore, I have traded for golden carrots multiple times, and their price has remained constant, while the pumpkins have not.