Adam you need to get your facts straight.
The paper you provided is based on the initial horn Armitage found. There is no mention that he has found other specimens. The biggest red flag for me is he has never shown the horn in question is actually from a Triceratops.
And the article didn’t appear in a peer review journal. It is interesting that they actually have a peer-reviewed scientific journal Microscopy and Microanalysis, but he didn’t submit the article there.