The input source is a stylus pointing device.

Note that this bit merely indicates that an input device is capable of obtaining input from a stylus. To determine whether a given touch event was produced by a stylus, examine the tool type returned by MotionEvent.GetToolType(int) for each individual pointer.

A single touch event may multiple pointers with different tool types, such as an event that has one pointer with tool type MotionEvent.ToolTypeFinger and another pointer with tool type MotionEvent.ToolTypeStylus. So it is important to examine the tool type of each pointer, regardless of the source reported by MotionEvent.Source.

[Android Documentation]