This gist demonstrates the difference between threading and asyncio. To be clear, they're both limited by the Global Interpreter Lock and are both single process, multi-threaded. They are both forms of concurrency but not parallelism.
Threading (via Thread, concurrent.futures) employs time-slicing of CPU. All threads are given a slot of CPU time to do work. If the thread is blocking (sleeping or blocked on sockets), then off it goes to the next thread. With many threads that are blocked for long periods, this begins to degrade into polling (polling vs. interrupt)