If I sell you some 2nd hand Lego bricks, the same logic aplies.
I am not affiliated with Lego, yet the thing I am selling was legitimately made by Lego a while ago. When I describe what I'm selling, I clearly say I am offering lego bricks for sale.
Here grubhub seems to be doing the exact same thing with food. Hard to see how one can be illegal while the other isn't.