Afternoon menu starts at 3pm here. (Forgetting that apres midi means after noon, not after 3pm). The menu does not say that anywhere. Don't plan your day around what they say they will serve. (You can have your weird rules, but at least communicate them in advance).
Waitress was friendly, manager should avoid accosting people about their experience as they're trying to leave.
Edit based on response: first, no it's not normal to be accosted by an unpleasant person who doesn't want to understand the issue, on the way out. Second, the serving times are NOT publicised on your menus until I complained. So dishonest. Note that you said when dinner starts (à partir de), but not when your invented post-lunch does.
AND you still haven't answered why you call it afternoon when it is apres-15h. You don't get to say "in France, what is after midday is defined differently and randomly based on when we end our meal service", especially because in person your excuse was staffing etc. I've been in France many times and people tend to know how to describe time periods reliably. Dont tar your country's culture with incoherence.
Also, don't be defensive - fix your problems, and also don't make changes to fix them and then deny you did.
