I'm assuming mounting will work similar to 4th gen games, so perhaps stealth attacks will be similar? Maybe its harder each time you try to sneak up on the monster, perhaps by the time the monster is near death, its almost impossible to sneak up on it unless its sleeping? Totally unsure too.
The stealth attack instantly led to a mount. I think the person you're quoting is right about it being a a special crit that only works once per fight. Maybe it deals extra damage and automatically applies the status effect of the women you're using (if it has one) and guarantees a mount (if it's a jumping attack)?
While they could have shown a lot more, what they have shown makes it pretty clear this is a Monster Hunter game with some tweaks.
Using your main weapon while mounting a large monster is a lot bigger than a tweak.