First off, the suggestion that it's "his agenda" that the group is bound by is incorrect. See the answer to FAQ#14 https://robertsrules.com/frequently-asked-questions/#faqs
Next, if your group has adopted RONR and meets within quarterly time intervals, the standard order of business (see 41:5ff) applies and there's no need to adopt an agenda.
If your group's bylaws or special rules don't define what a discussion item is or what an action item is, then it seems that the chair just made this up since those things aren't defined in RONR either, though we do see those terms used here by posters from time to time but I have no clue what they mean.