The key concept is buoyancy. A helium balloon has potential energy when it is at ground level because it displaces air upward. The air has gone up, so its potential energy has increased. When you let go of a balloon, the air rushes in under it, allowing the balloon to go up. The air ends up lower than it was, releasing the potential energy.
This has absolutely nothing to do with alpha emission, in fact alpha emission is something helium cannot do (helium is alphas)
Think of a cork at the bottom of a swimming pool. If you let go of it, it floats up. Where did it’s “reverse potential energy” come from? It came from displacing water. The water, being more dense than the cork, flows down around it, pushing it upward.
Helium isn’t special, it’s just lighter than air. There is no magic helium property without which stuff can’t be lighter than air, it’s just a density thing.