At the moment non-blocking is irrelevant because as you say it only serves one request. In the future if AWS implements request parallelism inside of one lambda that might be different (just to make sure I have no knowledge of them working on it, could just be something they might want to do at some point).
So its good to assume at the moment and my assumption is that FaaS providers will make you specifically say you want to parallelise requests in one function in the future. I’d be surprised if they do it out of the box.