I am sick of watching the English language decline. We (Americans), used to say, "Out for breakfast and/or lunch (never out to lunch). But we would go out To dinner (or to dine). These were the polite ways your grandparents spoke.. but somewhere along the way parents stopped teaching these things. It is a loss to our culture, and one of reasons why I am respectful of the French.
The audio (to my anglophone Quebecer ears) is clearly "Elles sortent". The singular version "elle sort" sounds different. "Elles sortent" sounds almost like it is one word ellesortent, and the ending on "sortent" has a TUH sound to it. "Elle sort" sounds like two distinct words, like there is a momentary pause between the two, and the ending on "sort" is a hard stop....almost like the T isn't there. Elle SAHR. I'm not very good at explaining sounds. Maybe try typing the two into Google translate and use the audio button to hear the difference. Google translate can give some very bad translations, but the audio is usually pretty good.
I thnk the google translation is much more human sounding and there is a clear clear difference. I find the voice of duolingo very unclear mixing d and b and n and m quite easily as well as the clipping of an obviously electronic voice being mistaken for a language sound I wish you would use a much cleaner human voice.
You are technically correct to use the gerund form, dining, but it sounds very awkward to a native speaker's ear. They go out to dine sounds more natural, though very formal. Most people (from western Canada at least) would say either "They go out to eat." or "They go out for breakfast/lunch/dinner/a snack."