Patent IP theft doesn't depend on intent. If Dr. Hon's work was later, as you further speculate, then Mr. Ritchie could present notarized, witnessed evidence his work came prior - which, in ~30 years, he has been unable to do.
He did not do so - which is not the same as if he was unable to do so. Mr Hon did not care so why would Andrew Richie? Both were interested in making folders more popular. At the time the issue occured (early to mid 80ies) they did not really compete with each other. If Mr Hon had filed a claim (which would have been the first step if he considered that Brompton was violatin his patent) Andrew Richie would probably have defended himself (or changed the design) and both of us do not know what would have been the outcome of a possible trial.