It sure sounds like there wasn't a "lock on the door". There is a significant difference between FTP and other protocols: FTP has specific support for "anonymous" sessions. There is even an entire RFC (1635, "How to Use Anonymous FTP")[1] on the topic.

From the article:

    I actually remember them having a passworded FTP site
    back in 2006. To get the password you would call tech support
    at Eaglesoft\Patterson Dental and they would just give you the
    password to the FTP site if you wanted to download anything.
    It never changed. At some point they made the FTP site anonymous. 

While there so no mention of the username involved in the anonymous access, it sounds like they switched from handing out a common password (stupid, but probably qualifying as "unauthorized access" for CFAA purposes. However, if the change where they "made the FTP site anonymous" involved the standard username "anonymous", then the server is offering access.

[1] https://tools.ietf.org/html/rfc1635