How is data collected?

Question

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Good afternoon, there is a fastcallmanager.com service. An application like callbackhunter is installed on a mobile phone, a code is put on the site. A visitor enters the site and leaves a request for a callback, and the manager sees an avatar from VK on his phone and immediately goes to his profile. So this is how the script knows what networks I’m on, I don’t want the manager to see my VK page, I kind of didn’t agree to this, I left only my phone number.
It doesn’t matter what phone number you leave, if you are authorized in VK from this browser, then whether you like it or not, the company manager will know your VK ID.
1. Who gives this data? Browser? VK?
2. How legal is it?