Is it true eating nuts seeds or berries can cause diverticulitis?

NO: High fiber has been shown, in some studies, to be salutary

Probably not: It was once thought that such things could lodge in existing colonic diverticuli or block their openings, resulting in inflammation and infection. There is no real evidence of it. Some doctors still recommend avoiding such foods, but it probably makes no difference. (Personal story: I had divertiulitis 35 yr ago, another episode 2 yr ago, no others -- and I eat these things in large amounts.)