Too close for comfort

I was driving south on Highway 65 nearing new Highway 20 on my way to work last week, and a large dump truck deal with an attached dump on the back was coming north on 65 with his turn-signal on, indicating he was going to turn east onto 20, just like I was. It appeared we were both going to approach the exit at about the same time, but I got there first. Well, silly me. I have no idea where this notion came from, but I always assumed if your turn signal is on, you’re going to turn in that direction. Right?