It's a linear reaction to the amount of force you apply. So it seems to be implemented in a number of ways. They demonstrated contextual menus, as well as peaking (holding with a bit of force) where you could then push harder to "pop" into the content or relax to go back to what you were doing.

It seems highly similar to the Watch — including the haptic feedback (which to me is an important part of what makes the interaction work on the watch).