We aren't trying to judge you, simply letting you know that what you heard was incorrect, and that to establish a good seat, you must be able to rely on your core for balance rather than your legs.
You should be sitting on your crotch, but your butt should be maintaining a contact with the saddle as well, which is where 'pockets of your jeans' comes in to play. There's about a 6" space on the horse's back where you will find balance and be able to ride correctly, and to be in that space, the best way is to be sitting right where the hem of your pockets will touch the saddle. Anywhere above the beginning of your zipper is too far forewards, anywhere past the hem of the pocket it too far back.
With your legs pushed up under you in what my trainer calls the 'duck squat,' you're forced further up towards your zipper, and your pelvis will tip forewards.
As for the trainers, I really don't find that to have any relivance. Just because you turn out good horses and you're well known doesn't make you a good rider, or an ideal for other people to copy. Take Linda Parelli for example. Plenty of people follow her, copy what she does, say 'oh well she does this...' but I honestly think that her riding is garbage. Now I'm sure she's fixed a few horses, she's obviously
got a lot of money and quite a pull in the equine world, but that doesnt make her any better of a rider than my trainer.
In that first picture, I actually think that his stirrups aren't as high as they appear. With the horse in that position, the perspective is messed with. They look fine to me, and if his horse were standing square I believe that his feet would sit right where they should be, high enough to touch the horse's girth, low enough to create good balance. The second picture is too small for me to see. Looking at other pictures of him though, almost all of them show him with nice, long stirrups. Not with his legs crooked behind his knee and pushed forewards at the ankle.
( pictures from SWTcutting