This is (err, maybe-- I'm not as sure now as I used to be) the cheap-ass version of PadTech's switch.
It uses two springs: a larger outer spring for resistance, and a smaller, shorter, inner spring attached to the bottom of the stem (it's hollow). The inner spring touches down on the PCB partway through the travel, making the switch. Naturally this is a much cheaper way of doing things than the more expensive version of the switch, where a magnet is attached to the bottom of the stem instead and a magnetic sensor reads its position.