This difference reminds me of when cooperative learning was big and teachers would say, “My kids work in groups all of the time.” Cooperative learning was so much more than working in groups. This seems like a similar comparison.
Here is a link that compares the traditional project assignment vs the process of PBL.

From:
What’s the Difference Between “Doing Projects” and Project Based Learning ?Image attribution flickr user josekevo; The Difference Between Projects And Project-Based Learning; © Amy Mayer, @friEdTechnology, The Original WOW! Academy, http://www.friEdTechnology.com Please copy and use freely!