I see many single-page portfolio WP themes. How are these built?
Are they built using pages for each section? Is each portfolio piece it’s own post? Or is everything done through a customised theme-options page?
What is the standard here?
I don’t think there is one standard here. Everyone probably uses their own methods for creating one-page themes. How I would do it, keeping in mind that I like things simple, is I would create a bunch page templates, each corresponding to different section of the one-page (like gallery, portfolio, blog part, slider part etc.) and then just order them using the ‘Menu order’ in page attributes. Maybe even build some kind of drag-and-drop interface in theme options.
As I said, I like things simple. Other may have some more advanced systems with content composers and whatnot.