The thing this is most similar to is Twitter's recent 2FA implementation. Except, instead of the site automatically pinging the app to open on your phone (and then you ACKing or NAKing the ping), it requires you to open it yourself and scan a code on the screen (thus implicitly ACKing it.) Everything else happens the same.
It seems like the basic idea isn't unique. I was thinking of something similar a while back and found https://tiqr.org while looking for similar ideas.
