It works in a plane, so it’s somehow able to detect the higher rate of speed, maybe by integrating, but I think it does use signals from CarPlay as well.
From an accelerometer's point of view, there is no observable difference between standing "still" (on earth's surface, moving some km/s around its axis, which also moves around the sun, which also moves around the milky way, which...) and being in an airplane. Both feel ~9.8m/s/s acceleration in the same direction because both are in a moving reference frame that stands still with respect to the accelerometer. The 'absolute' speed of the airplane (relative to the ground or air) is not something the accelerometer can measure, so it couldn't not work at 'higher rates of speed'. (If I understood your comment correctly!)