It uses layers, the same way a phone keyboard has a separate layer for numbers and symbols. Holding down one of the three thumb keys on either side activates a new layer. Since you can use your thumb and fingers at the same time, there’s no lose in typing speed. Indeed, the layout puts numbers and symbols closer to the home row on a layer than using a physical number number.

For all symbols, you would have needed a shift-modifier to access those before. With this design, the symbols are closer but use a layer switch key instead of a shift key to access them.

Everyone who uses a phone keyboard has learned a new compact keyboard layout. It’s not so hard.