I don't think that's what he's talking about, the horns can easily just have no hurtbox.
Problems arise when I make a giant Patroklos, for example. Will he have a giant leg and therefore a huge 1K range? It's impossible for this to NOT cause problems with balance. They could avoid this problem by keeping the hitboxes the same this only creates more problems. If hitboxes were the same and I used a giant Patroklos I'd have to make 1K deeply clip through the enemy character if I want it hit at the normal range. They'd have to change the animation for the move if it is to have to the same range. Even then, unless the hurtboxes are also unchanged, the move will behave differently since the distance between the hitbox and hurtbox is now different.
And if the hurtbox isn't different, we would still appear to have wonky hitboxes. Just imagine a giant vs. giant if neither hitboxes nor hurtboxes are changed... you'd be fighting inside each other half the time.
So we can safely conclude that hit/hurt boxes will be affected by size changes. Big characters get more range likely duckable or STCable mids while small characters will probably screw up combos/tech traps and thats it.