If you take the time to think logically about it you'll see that that is a load of crap.
Wild splendens (since I assume your book was not talking about other species) are bubblenesters. They have to have a secluded, safe spot to build their nest that will be safe from potential preditiors. They'll make their nests among the rice paddies where the nests are unlikely to be seen from above.
When the fry hatch they'll need to swim around to look for food... there will be little to no food in a hoofprint. Also in a hoof print they'd be very vunerable to predation. Just as domestically raised betta fry hid in the plants provided, wild fry will hide among the plants and leaves in their habitats.
Once upon a time I heard that bettas have been found in oxen hoof prints because they used the prints to jump from one paddy to another. THAT would make sense, especially considering what prolific jumpers wild betta are. They have to jump out of the water to catch insects yes, but jumping their way to a different habitat makes sense as well. That's how species spread.
Edit to add...
It's also possible that mouth brooding species have been found in hoof prints (while moving to a different location) and have released fry in those prints and that is how the rumor got started. That's just one of my theories... I've never heard/read of that being the case.
Dont think a hoof print could sustain 'a' fish let alone a family of fish. Ammonia builds in our tanks pretty quickly so I would have to say that it would build in a hoof print much too soon for betta to spawn in there. I agree with 1fish2fish that it is possible that a mouth brooder may have been found with a spawn 'travelling' or making a stop over in a hoof print but I just dont think that such a small amount of water could sustain life for too long.
Then again......It rains there.....alot. It is possible that they could spawn and then the hoof print would flood over releasing the fry into another area of water.....possible, unlikely, but possible.