The “silver guy” might be a Hall effect sensor or reed switch to detect when the case lid is closed.
When you get back to this step as you are reassembling it, it's tempting to test that you've got all the cables plugged in properly by switching the phone on and testing it. However the Home button will not work until the front panel is back in position, because the electrical connection is done by a pair of touch contacts which only work when the phone is assembled.
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