What does the comma between the last two nound in this news heading mean?

It’s a specific type of shorthand you see almost exclusively in news headlines. It means “and” - the sentence reads “Grubhub to pay…against customers and drivers”

Typically you will only see it at the end of a clause. For instance you might see “Gorilla beats chest, drum; musical talent lacking” or “Gorilla beats chest, drum. Musical talent lacking.” And they both more or less mean “Gorilla beats his chest and a drum, but he doesn’t have any talent.” (Though the first example is more correct). However you would not expect to see “Gorilla beats chest, drum, musical talent lacking.” That would mean that the gorilla beats chest their chest, a drum, and they also beat their musical talent which was lacking. It is obviously nonsense

And

here's a great blog post i read last year that outlines many rules used to write succinct headlines: https://www.englishnewspod.com/blog/cracking-the-code-understanding-news-headlines-in-english/

Ancient post resurrected by boredom, curiosity.

Yes, the comma essentially takes the place of an ampersand. However, I can assure you it did not originate as a “clickbait” strategy. Predates the Internet by quite a bit.

I’m not sure where this grammar originated or what it’s called, but in my memory I’ve exclusively seen it in headlines.