The client has been SIGKILLed, so it’s not assuming anything. I wonder whether the comment is a typo and they meant to kill -9 the server instead.
replyHypothetically if this was HTTP without a Content-length (like it used to be in the olden days), you could have a proxy server assume this is the entire file.
replyPerhaps a permanently hung connection because timeout is zero (=disabled?)?
replySeems plausible since FIN only means “I’m done sending” also called a “half close”.
replyFTP has different data and command connections so the server may not have an outstanding read to detect the data connection break.
But.. it should still clean up both when the command connection dies