"The lunch finished five minutes ago."
Translation:El almuerzo terminó hace cinco minutos.
Hi Wim, your sentence should be accepted as well. I'd report it if I were you.
I'm not an expert in grammar, but from my point of view (native speaker here) the only difference between your sentence and the one suggested by Duolingo would be that if we say "El almuerzo.....etc." the fact that the lunch finished is central, while if we say "Hace cinco minutos..." it gives the impression as if you were highlighting WHEN it finished.
But well, that's just my personal opinion as a native speaker.