Actually, you all are right. Bluejays can be mean and dive-bomb dogs and people. What happened was he saw the (empty) bird feeder at the edge of the woods. Jays will make hawk calls to scare off the other birds, or whoever happens to be around, and then just mosey in and have the feeder to themselves. It's a pretty handy adaptation if you're a Jay, but not so nice if your a paranoid Yorkie mama.
So glad I made a few people smile on a Monday morning. Have a great day everybody.