Photos-Moments

If you deleted all data, there should no longer be a Photos library at all. The Moments are a part of the Photos Library. The Photos Library should have been deleted from the Pictures folder.

Before selling a Mac, erase your system volume completely and reinstall MacOS X, as described here: What to do before you sell, give away, or trade in your Mac - Apple Support

Your Mac should be reset to the factory settings, just like out of the box, when you first set it up,with no applications you have purchased installed. And check your backups, if they are readable and working, before wiping your Mac.

Yes. Just follow the directions in the Apple document What to do before you sell, give away, or trade in your Mac - Apple Support  like léonie recommended.

If you have been using the Photos.app and want to delete all photos you have just to delete the Photos Library.photoslibrary from the Pictures folder. But to be sure, that no personal data are left, the safest way is to boot into the recovery portion and to erase the system drive. Then install the system again and do not create new user account. See step 7 in this document: What to do before you sell, give away, or trade in your Mac - Apple Support

How to erase a disk for Mac - Apple Support