On firmwares 7.00–12.70 (slopkit: poops and p2jb), the autoloader uses a custom version of elfldr that only accepts connections from the PS5 itself (localhost). This improves security by preventing unauthorized devices on your network from sending payloads to your console. On firmwares 1.00–5.50 (umtx2), the stock elfldr is booted.
If you want to use a "normal" ELF Loader that allows sending payloads from any device, you can simply load it through Payload Manager.