I'm pretty new to the whole speedrunning thing, and I was practicing my superslides. I can't remember exactly what I did (at all), but here's what I do remember:
1. I had farores wind on B.
2. I was an adult.
3. I did a lot of rolling and picking up bombs. Think of failed super slides.
4. I used farores wind once, doubt it had an effect on the ground jump, but info is good.
5. I did a lot of shielding the bomb, and backflipped when a bird from lake hylia hit me, and a bomb blew up at the same time. (shielded both hits. I think)
6. I drew my bow, shot the bird while L-targetting.
7. After I shot the bow and stopped L-targetting, I ground jumped. Just straight upwards. (I may have backflipped to cause it. Can't remember)
So yeah, I'm not sure exactly what happened to get the ground jump. I'd reckon it'd be the bird and bomb hitting me as I backflipped and perhaps the recoil was something.. IDK. But ground jump is possible, and anybody who feels they want to attempt to figure out HOW, go ahead.
Or it may already exist and I'm being dumb here, but whatever.