I was actually curious about parent's friend's idea. To be fair all these apps haven't yet figured out the whole market, so perhaps instead of genius we can call them 'implementable'.
I have seen an integrated system in Australia. Delivery Hunter. Actually involves a delivery service if restaurant does not have one.. We all thought it would fail but it is getting bigger and bigger.
In Aus, Menu Log and Delivery Hero are the main two with similar functions. They actually work with restaurants to integrate their existing online ordering systems into an integrated mobile app.
The original was http://waitersonwheels.com, which I used in the 1990's. It started as a catalog-based service, which waiter.com knocked off and improved.
It's not a defensible business model unless there's some exclusivity agreements with restaurants on the menu. (too tasty to resist.)
https://www.crunchbase.com/organization/deliveroo https://www.crunchbase.com/organization/just-eat https://www.crunchbase.com/organization/hungryhouse-co-uk