Taking the lane in a school zone?

Could use some advice here. My adult son and I both ride (he commutes, I don't), but in this situation I'm the driver.

Rider is in and maintaining the right shoulder in the image. I am driving in the right lane and slowing to enter the active school zone. I am in traffic, but there is room to my left so I move a few feet into the left lane to provide extra buffer for the rider, as I always do.

We both enter the school zone at about the same time. Immediately after entering the school zone, I see the rider who is maybe 3 feet in front of me begin to unexpectedly take the center of the right lane without a signal or appearing to look. I had enough room to avoid him, but he took a swing at my passenger mirror and was yelling. I slowed, and he proceeded in front of me, and then proceeded to take the center of the left lane (without signaling).

As we are traveling roughly the same speed, I roll the window down and tell him "You've got to signal so I know you're taking the lane" to which he replied "No I don't, read the law a**hole". I replied "You can't ride in the left lane. You're going to get yourself killed" to which he relied something again about him being able to take any lane and that I should read the law and then flipped me off.

So my questions are:

1. On this road, is there a reason you'd take the center of the right lane? As both a rider and a driver, I wasn't expecting it at all, and it was really out of the blue.
2. Do you signal (or at least look) when taking the center of a lane from a shoulder or bike lane? As the driver, I had no idea he was moving out of the shoulder here.
3. If traffic slows in a school zone, do you take the lane since both vehicular and bike traffic is at roughly the same speed?
4. Do you ride in the center of the left lane (or any lane other than the right)? In PA, this is illegal.
5. Did I do anything wrong here?

I believe he was eventually making a left turn much further up the road, and was using the slower school zone to attempt to cross lane (or maybe was attempting to ride in the divider).