iFixit found that the Smart Keyboard is water- and stain-resistant mostly because of the “high tech fabric.” It completely covers the keyboard, leaving no gaps or spaces. This means that in order to get underneath the fabric, cuts and tears need to be made, making a teardown irreversible.
Once the fabric is removed, you can see that Apple uses the key switches similar to those found in the 2015 Retina MacBook.
iFixit also found that the plastic frame has tiny vents, presumably to release air that may be produced whenever a key is pressed. The keyboard uses a 32-bit RISC ARM Cortex-M3 microcontroller. And instead of wires, Apple uses what iFixit calls “conductive fabric” that can better withstand constant folding of the keyboard case.
You can see the complete teardown at iFixit.