The process is called gating and amounts to the radar not starting to listen for some number of microseconds after pulse transmission ends. If you zoom way in and turn up the gain you can see the circle some distance around the display center that represents the gating distance.

That said, any reflector - mast, rigging, radar reflectors - will contribute to the return "smile" you see when close to a large target (like a commercial ship). The "smile" is a combination of the beam pattern of your radar array and multipath from local reflectors. An entertaining example is to pass between two anchored ships. You will see one or two "ghost" targets beyond each of the ships from the reflections of the signals back from each ship.