Who knows unless you have a router that shows all connections. If you are using a router, in the Firewall section or the LAN section it may have filtering. It might say "Allow" or "Permit" and in there you would enter your own device MAC numbers which will allow you and your devices but block any others. It also might say "Block" or "Deny" and there you would enter the MAC numbers of devices you want to exclude but allow all others. It's better to white-list (permit) your own devices. Your neighbor will see you have a WiFi operating but will never be able to connect if you "Permit" only your own equipment.