Difference in PDF Export

In Draw, what is the difference between Export as PDF and Export Directly as PDF?

Export as PDF allows you to set options (ie type of PDF, image compression, check for accessibility compliance, etc) used during the creation of the PDF file. Even if you wanted the default set of options you would need to clear that dialog to generate the file.

Export directly to PDF uses that predefined (default) set of options for the new PDF file. You will not see the options dialog and the pdf file is created without any further need for interaction (other than to give it a name).