Hi M.,
I don't agree with the poster who believes it's part of being a boy. I don't buy into the boys will be boys and are meant to behave badly mentality. THere's nothing in a boy's biological make up that's different than a girl's which makes them drop their food off their plate. It is, however, still normal for the age.
My take on tossing the food is that he's done eating. If he was actively eating, he wouldn't be throwing his food. As soon as he throws something, I'd declare the meal over.
Kids at 2 years old also don't always realize that if there's something on their plate or tray that they do not want to eat, that they don't need to throw it, drop it on the floor or otherwise get rid of it. Since you have an older child, maybe you can get her on board to help you with some role playing. Have her keep something on her plate each night at dinner that she's not going to eat, have her tell you, "Mom, I don't want to eat the rest of my carrots," and tell her, "That's okay, just leave them on your plate" and see if your son catches on.
GOod luck!