They are async across operations that do 'yield', i.e. when the function eventually runs an i/o operation or sleep or similar. Those are the points where the functions can be interleaved. Simply awaiting another function is _not_ one of those points: await here only means the called function might yield to the scheduler at some point in its execution (it doesn't have to!), not that the calling function will yield immediately.
Tasks are async funcs that have been spawned with asyncio.create_task or similar, which then schedules its execution. A timer of zero doesn't spawn anything so the coroutine just executes in the same frame as the caller so yes it essentially a noop.