No, it's a music reference indicating speed. In writing music, a 'bar' is a measure of time. There are usually four beats in a bar, so 'Eight beats to the bar' means that there are many blasts of the whistle in rapid succession - perhaps meaning that a train is about to leave soon or is travelling fast.

That is an old classic song ' Beat me Daddy, eight to the bar '. Andrews Sisters. Su.Ki explanation is perfect