It has a lazy Susan in-between your arm and the shield. This also lets you spin it fabulously for celebrations.

Clearly it's a handle grip, not strapped. Most shields are, it gives greater mobility and utility.

Not every shield is strapped down. Though I agree this one is a bit big for just a center grip

Not pictured: dwarf yoga

You could rotate it before battle to your preferred position, but not rotate it mid battle.