Connection with other Mac's and potential runoff of my files

So I went to a friends house and he has 2 macs. He also has this wireless network and i think when I connected with my Mac i also connected to his wireless hard drive. He told me he has something that is a router and a hard drive at the same time of something.

So as i checked his mack there was a Time Machine backup running. And i found it strange. Was it running because it was taking stuff from my mac. Or was it running cause it made backups irrelevant to me and i just happen to see it at that time? (now my time machine is switched at off can this setting change when you connect to others) I haven't set a time machine on my mac books so am i safe?
And in my mac's finder i could see down at the SHARED section i could see connected wirelessly a mac book symbol with a name and a hard drive called backup.
And i could see some of his files like Shared downloads and torrents (not sure)

1)So what happened and I got connected with him?
2)Is it because i put the his password in the wireless and i got connected with everything?
3)Is there a possibility that his drive or mac book could back up my data automatically and if so which ones?
I dont understand how this works...
If there is someone that can explain it to me ill be glad thanks!

righton said:

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So as i checked his mack there was a Time Machine backup running. And i found it strange. ...

Click to expand...

Strange why?

Because he backs up his computer and you don't back up yours?

If Time Machine was running on "his" Mac, it was backing up "his" Mac to "his" external hard drive. It has nothing whatsoever to do with your computer.

Thanks for the answer! Ohh ok i think i understand how it works. Sorry for being such a caveman with these things.
So my time machine says not configured and off so there is no way it might back up to anywhere. right?
So next question. Which files are shared every time you connect to an other mac or in this case to a wireless network and a wireless drive?

No files are shared by merely connecting to the same network unless you have placed files in the 'Public' folder or you have turned on File Sharing and purposely shared a file or folder.