I had a look at http://www.iana.org/assignments/port-numbers and 53300 doesn't seem to be a well known port. Nor did google return anything, of signifigance. HTTP does not redirect to another port.

First... are you sure port 53300 is not on their side, or a loopback, or a service you've moved to that port and forgotten... you appear to be running an FTPd so it could be one of the FTP data ports, usually a range over 1024.