Left subscription to the channel through the mass addition of users. How does this happen?

Question

Telegram

Actually a subject. It was like this: I open the desktop cart and oops, some kind of left chat appears in my contacts, to which I did not subscribe. In the chat history, a certain user "Deleted account" massively adds people in batches. Here, as it were, it is quite obvious that cheating works, but how does it work? I am attaching a screenshot.

spoiler

Answer 1

Because by default, anyone can add you to any group. But in the settings there is an option that only your contacts can invite to groups.