Which creates a hidden service addrwhatever.onion. Later somebody
connects to addrwhatever.onion:8333 and the tor daemon opens a TCP
connection like 127.0.0.1:46153 -> 127.0.0.1:8333. Next, some other
application (not the tor daemon) connects directly to 127.0.0.1:8333
and that is 127.0.0.1:52490 -> 127.0.0.1:8333.

What if the application running at 127.0.0.1:8333 wants to distinguish
incoming tor connections from the rest? From its point of view the
connections from the example above are just TCP connections coming from
127.0.0.1:46153 and 127.0.0.1:52490.