How can next door be connected?

[Gavin78]

I have my own router and I recently setup an older router in AP mode so that I could have it upstairs to help boost the signal with my wifi cameras.

I noticed when looking at connected devices which should have just been the cameras.

Those that live next door to me recently had sky installed and on the network band 2.4ghz it said this (sky light digital limited) was connected to my AP router. I could see it on the network but no option to kick them off. I then tried to put it on the band list and it was still connected.

It's password protected I looked into the router options to see if there was something setup during the AP process allowing other networks to join but I couldn't see anything.

In the end I changed the password on the router and noticed it had gone although I didn't leave it on long enough to find out if it would rejoin the network and unplugged the router for now.

The thing is the wifi password is same as the one I have setup downstairs so I figured if they had cracked the AP router they would have been connected to the one downstairs a long time ago.

I posted online and someone said (ski digital) is a photo frame or something like that but I'm not sure. Hoping someone on here might have an answer?