23 miles in 50 minutes, or about 27.6 MPH.

That would be really fast. Downhill?

On the other hand, if one-way vs round trip was mixed up, and it was actually 11.5 miles each way in 50 minutes, and 14 MPH average in traffic, that would be possible for almost any avid cyclist (depending on traffic and lights and how often the rider fails to stop for signals).