Debugging Postgres error: "could not send data to client: Broken pipe"
Yes, it seems like you've understood this correctly. The client sent the data to a postgresql backend, and then abruptly disconnected (or was killed). The message is basically "I have an answer for you, but I have nowhere to send it!"

I would definitely look at the logs of the other services and compare timestamps to try and look deeper into what is going on.

Hope that helps. =)