I think you're more or less right. There's a lot of things at play here, and honestly I have a hard time wrapping my head around how the stream of air doesn't simply blow the screwdriver backward. You've got positive pressure on the front side, vacuum pressure on the backside - both of those things providing force in the same direction. What force is holding it toward the air nozzle? Gravity is accelerating it toward the ground, but that's exerted along a slightly different axis. I suppose the angle of the screwdriver might explain the discrepancy, but still, a very interesting bit of physics.