The Register link in the WishList Member Widget directs to the set Non-Members page.
The Non-Members page is where users will get directed to if they do not have access to the protected area they are attempting to view.
The thought behind having the Register link on the WishList Member Widget direct to the Non-Members page is that you will likely have a link to register on your Non-Members page.
This is because you will likely want to provide the option for users to sign up and register on the Non-Members page as they have shown they want access to the protected content because they clicked on an area they did not have access to.
Also, you may have multiple levels available for registration. So with that Register link on the WishList Member Widget directing to the Non-Members page, you can then have multiple links to multiple registration forms display when the user arrives.
As a note, you can set the Non-Members page in the Settings > Configuration > System Pages section of WishList Member.
There is an option to remove the Register link from the WishList Member Widget.
This can be done in the Appearance > Widgets section of WordPress.
You can click the box that allows the Register link to be shown or not in the WishList Member Widget settings.