In the software world, we often write software that interfaces with other software. Let's assume I wrote program A, and it interfaces with program B that John wrote. When communicating with John about the interface, I might say something like: "When program A sends message X, you respond with Y". Or even: "When I send message X, you respond with Y".
Obviously, I am not sending these messages, and John is not responding - program A is sending to program B. It's just often easier/less verbose to basically substitute the author in place of their work.