Two things:

Vectors: Remember computing vectors in high school math? (I can, and I'm pushing 60.) Or have you at least played billiards? In a collision between two moving bodies, body with the least energy (me at 190 pounds including the bike moving at 15-20 mph) will be propelled at an (easily computed) angle by the body with the greater energy (4200 pounds of Pontiac moving at 10-15 mph). Plus, by steering to my right around the front of the car, I would already have started to move in the same direction of the car, reducing total impact.

If I hit the side of the car, all of my energy would have been converted into impact and injury. Choosing the front of the car, some of my energy would keep me moving away from the car, plus some of the car's energy would be imparted to me, also pushing me away from the car.

What I didn't clearly state in the post above is that this was on a four-lane. If we count from the bus, 1, 2, 3, to 4 at the other curb, I was hit in lane three. I continued moving forward as I barrel-rolled though the air, and landed in lane 1 in front of the bus, well away from the car and out of further danger from it. I was also vectored to the right by about 20 feet.

Impact, injury, and chance: There was a 100% guaranteed chance that if I chose running head-on into the car's front wheel, I'd end up flying across the hood, perhaps getting ripped open by the radio antenna or windshield wipers, and/or smashing through the windshield. Then If I did go through the windshield, being carried down the street until the driver slammed on the brakes, ejecting me back across the hood and into the street, or (if I was lucky and didn't stuck get in the windshield) falling off the other side of the car into the street. 100% chance of major injury.

The alternatives were a possibility that the driver would realize his mistake and stop, or failing that, I'd bounce off the front (vectors, remember) and have to deal only with injury from falling into the street. 50-50 chance of minor injury.

I went with the 50-50 chance of complete escape or minor injury. I got the minor injury.

Had the car been further ahead into the turn, BTW, I'd have tried to steer around the back. Such was not the case.

And it's not all quick thinking. I pay attention to every collision report here and on other forums, even if I don't comment. Over time, I've built a list of "What would I do in this scenario?" and filed the answers away. It was simply remembering, "Left cross, not enough room to brake, won't make it behind, might make it in front" and executing.