They are completely unrelated. Popular projects is a way to advertise services you might offer that fit into a product-like box (for example, as a writer, I could put a price tag on blog posts of a certain length). It's just another way of showing a client what you can do for them and what it might cost them. It doesn't have any connection to specific past projects and doesn't show samples.
Your portfolio is for showing work you have already done, so the client can see whether he likes your work.