A hundred years ago on irc someone from Russia was describing their internet connection, which was ethernet, while I had only ever heard of dial up outside of large companies. It was just people had set up their own hubs and switches in their appartment buildings and strung cables between buildings. This blew my mind. They just ran themselves ethernet and everyone got a drop from a switch in their building. It wasn't…
Not at all.
Even in the US, rural folk have been beaming directional wifi to each other for a couple decades now (at least), and sharing utilities by personally running electrical, coax, telephone, or ethernet throughout a shared building or across houses stretches back for as long as those services have been available.
Sharing ("stealing") Cable TV by just running coax around was huge before those systems transitioned from simply using sometimes-encrypted broadcasts to a more authenticated/addressable scheme. For decades, party lines (for the telphone) were both official installations from the telephone company and de facto local networks run by one's handy neighbors. Countless people punched ethernet between walls in apartment units just the way you describe to share upstream connections. Same goes for power in squatted urban units or among trailers/shacks where they would be clustered tightly.
What made it unfamiliar to you (and perhaps many here) was probably just the class and finances of your family and the people they mingled with.