Deno.serve vs serve (from @std/http/server.ts)

This is probably a newbie question, but why does deployment end with an error during the warm-up step when using serve from the standard library? As far as I understand, this happens due to a timeout because the server is listening on port 8000. But then why does Deno.serve deploy without any problems? Does this mean that they have different way of starting the server? If someone could explain this in detail, I would be very appreciated.