The terminal ileum is but a small, small portion of the small bowel. The small bowel comprises more than 20 feet of intestine; the terminal ileum is just the last bit.
The article you posted is interesting. That author identifies three important reasons why pathological findings of "non specific inflammation" might be related to improper procedures during the scope or in communications between the GI and pathologist. It is on the 2nd page where he notes that IBS can also have "non specific colitis" that I found surprising. See this info from Mayo about
IBS:
www.mayoclinic.org/diseases-conditions/irritable-bowel-syndrome/basics/definition/CON-20024578G.J. Mantzaris says, in the article you linked, that the histology of "non specific colitis" is unlikely to change over time for people with IBS. Meaning, I suppose, that this is a condition which will not progress.
So, you went to the DR because you have struggled with bowel problems, focused on tenesmus and frequent bowel movements and they have disrupted your life. Your DR has found inflammation in the sigmoid colon. You and your DR may decide that this is "IBS" and that the only treatment you should work with is dietary and perhaps an antispasmodic to relieve the tenesmus. That is absolutely something you should feel free to pursue. What I've been trying to communicate to you is that there are ways of treating inflammation in the sigmoid colon that could provide significant relief to you, should you decide to call your condition "inflammatory bowel disease."
In a few years you may find that nothing has changed in your bowel. Or maybe not; maybe in a few years the inflammation will have become different in some way. I'm not a doctor and I don't know how else to interpret what you've told us.