How does pedaling power transfer to the bearings in Hollowtech II bottom bracket?
You seem to be assuming that "power has to be transferred to the bearings". That is not the case. There is no "interlock". All that needs to happen is that the crank spindle can spin with low friction. 

As you pointed out, the inside of the bearings is smooth and so is the spindle. I guess it's possible that they slip relative to each other, but so what -- the spindle/crank still rotates, the chainring rotates, and power is transferred from the pedals to the crank arms to the chainring to the chain to the rear wheel.

In practice, the friction between the spindle and the inside of the bearing is probably greater than the friction between the inside of the bearing and the outside of the bearing, and therefore the bearing spins.  I assume this is the case because the bearing is designed to have low friction, while the spindle inside the bearing is basically like a shaft inside a bushing (a cylindrical hole), which has more friction than a bearing; otherwise we would not use bearings.