Delegating a project is (theoretically) the same thing as delegating a singular task. With a project, the delegator becomes the project sponsor and the delegatee is the project manager. With GTD, there is a low threshold for something becoming a project because questioning "what is the next action ?" turns what is ostensibly a simple task into a project. For example, I hire a cleaning lady to come to my house. This is a project for her as she has her lists of tasks to do. It's also a project for me as I have multiple tasks to do (i.e., be sure her money is on the fridge door, be sure I have all the supplies she needs, be sure I have my "amorphous blobs" of "stuff" put away.) There are contingencies in this project. (She called me last week to tell me my vacuum cleaner started billowing smoke.)
On a bigger scale, I am having my hardwood floors refinished. I have delegated this out to a vendor who will project manage it. Just like with my cleaning lady, I can't just write a cheque/check and put it in @waiting-for. I was going to be out-of-town while this was being done but the vendor wants me to see the colour of a test spot to be sure that I like it. Thus, I am being assigned a task by the project manager, that I, as project sponsor, have delegated to!
My understanding of this is that in GTD, we can be a project sponsor and delegate the project management to someone else. However, there are often multiple tasks in being the project sponsor. Paradoxically, these tasks become a project by the GTD definition of project.