To me, yes, fingers pointing towards the sky is hitting up on the ball.
The "spring board / yo-yo" technique isn't too complicated and I think there are several ideas about how it's accomplished. It all happens in a split second at the exact point where the thumb exits the ball, the hand opens up, the weight of the ball on the fingers forces the fingers to bend backward slightly, and then the speed of the swing flings the ball forward off the hand.
Another source of imagery, imagine holding a pail of water filled almost to the top with water.
***First things first, most people would not use their thumb to hold the pail, just their fingers.
Then, imagine going to the foul line, releasing the pail onto the lane so smoothly, not a drop of water is spilled. In fact, the water doesn't even ripple. The amount of swing force would project the pail 32ft down the lane. (We're assuming there is a medium, fresh oil condition).
There is one other visual I use when working with bowlers.
Imagine holding a softball in your hand, going through the approach, and throwing the ball underhand 60 ft. Key(?) The softball must remain exactly 2 inches above the ground all the way to the pins.
Those are the visual / mental techniques I use when coaching. All are the direct result of working with various types of athletes from other sports who have decided to take bowling a little more seriously.