I don't know where this rule comes from and can't find any citations, but there are several sentences using tepagon with a third person recipient on the wiki, and this course itself only uses tepagon on the page explaining the dative case, and uses it with third person recipients: https://www.duolingo.com/skill/hv/Dative/tips-and-notes. So it might be some earlier idea that Peterson had that was forgotten or discarded, applied inconsistently, or not even an actual rule at all.

Edit: I also can't find any sentences using irughagon, but many with tepagon. So irughagon itself seems quite forgotten.

Edit 2: Some news on this issue: https://dedalvs.tumblr.com/post/180601132580/what-is-the-difference-between-tepagon-and It seems the rule is still valid, just applied inconsistently.