you are correct
I bought a new router because to my dismay, my three year old router was dropping the internet on my wife’s computer
I hooked it up and the my web account produced a graphic showing the stuff receiving and transmitting. There were 10 devices!
There’s just me and my wife. I really had no idea
You need to get some expert help with your router. If you don't lock it down, anyone nearby in the neighborhood will piggy-back off your ISP connection. Best way is by hidden router name that only you know and can type into your computer in initial connection, along with a strong password. Additionally, you can limit the number of connections allowed to a small number. Additionally you can only allow a small list of IP addresses to connect, that you type into your computer rather than have the router randomly assign an address (if you are real paranoid).
I use a Netgear Wi-Fi router and it comes out of the box with password protection on the Wi-Fi. Was yours wide open and unprotected when you got it?