Could it not just be a centering pin that actually presses down on the switch on the PCB?
That isn't a metal ring around the home button is it?
Perhaps it's a prototype that got sent out by accident, perhaps with the beginnings of the touchID hardware?
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The ring around the home button looks that way because I have the MIME glass screen protector installed. It's makes the home button a little recessed looking but has curved edges and is by far the best screen protector I've had for any ipad I've owned.