First of all, keep in mind that, like any scanning service, the Symantec site may not always be 100% accurate. You may want to ask the authors of the firewall you are using for another reliable site that you can use.
All the companies that provide such tests do use the result pages to include advertising for their products. The fact that I included a link to the Symantec site in my article is not a "recommendation" to use their products : you know best which firewall suits your needs.
However, having ports 20-21 open is, unless you have turned FTP on, both abnormal and dangerous.
Indeed, this may indicate that you are running ( knowingly or not ) an application that listens to these ports and is ready to receive or transmit data. Would you know which application could act in such a way, try to uninstall it and see if the results change.
As a test, you may also want to disable the third-party firewall you use and to turn the Apple one on temporarily... Does it change the test results ?
Let me know if this helps !