Suspension points are a dynamic, whole-program concept: they're the places which cause the task to actually suspend and abandon the thread.
Potential suspension points are the static, conservative, function-local view of suspension points: they're the points in the function where a suspension could potentially occur and therefore the function ought to be prepared to abandon the thread. Any dynamic suspension point is always "inside" a potential suspension point from the perspective of every async function on that task: all of the outer functions must be awaiting an asynchronous call, and the innermost function must be awaiting at the actual dynamic suspension point. From all of those functions' local perspectives, the exact reason for the suspension (which may be N levels of call deep) is much less important than the fact that a suspension is possible at that point in their execution.