Well, IMHO (no offense meant), memorizing programming manuals makes one a good lonely programmer.

To become a 'professional software engineer', one must learn to be a team-player within a group of persons tasked in building and maintaining a piece of software that will stand the test of time. Which requires a very different skill set. One can be a good SE and still be relying on auto-completion and inline help in one's favorite text editor.

Remembering the API of your languages definitely helps, but actually building softwares that will be used by real users, for years, that's what makes you a 'professional software engineer'.