Well I think he mentioned in the guide that you don't need to be able to hold one-hand handstands to be able to do one-hand solar eclipses. I don't remember because it's been a while since I last read that guide, and I'm lazy to pull it up and read now.
Anyway, you have to know your balance on one-handed handstands pretty well to help you do one-handed solar eclipses. It doesn't mean you have to hold it. Personally, I know how to balance but my arm isn't strong enough to hold me up for too long. It just means you have to know when you're about to fall left, fall right, or whatever. So if you're falling to the left, your next hop should go left to counter it and stay straight.
As an exercise, I recommend trying to get into a one-handed handstand from a standing position, without any assistance from your other hand. That means, you put only one hand down and try to get up and balance like that. It'll help you master balancing on one hand. You know that trick people do sometimes to stay balanced on two-handed handstands, where they walk? Try to do that with just one hand, and kicking your legs up to help you do so.
Be careful, though. Know your limits, because if your elbow gives way (like mine did when I was too tired but kept trying), you might fall on your face. ;(
