Yup. Pinterest is less about saving the URLs/pages, than about curating a selection of pictures and visually displaying them in a fashion-magazine looking manner. Pinboard doesn't do that last I checked.

Actually, plenty of people use Pinterest as a way to save curated lists of URLs/pages. My daughters use Pinterest to make Christmas lists. my wife has used it to save interesting looking recipes. Sometimes the display is core, sometimes it's a nicety that makes it easier to browse.

I would hazard that the number of people looking to save bookmarks online easily is a couple orders of magnitude more than those looking for fashion magazine layout, at least.

Beyond that, it's pretty easy to slice up aspects of two companies so they are or are not competitors. I think Pinterest and Pinboard fairly clearly are (and since Pinterest is often mentioned along with Pinboard, I assume others think so as well).