They will link it by statistical analysis of the networks of your friends that use WhatsApp and/or Facebook. Many will have uploaded contact details, others may have uploaded your email addresses etc. Its not a hard problem to solve. They may not get your full name, but that's not what they actually want. They will have a unique identifier for YOU, and it will almost certainly be right. Ditto, and with bells on, what google is capable of doing. It doesn't matter if you never ever use anything by google, chances are very high that if you use the internet, there is a unique identifier in google's system with an electronic 'signature' that matches you.
Take a step back and imagine the data trove that Google can have on almost anyone, even someone who tries to be 'dark'. If you are a casual non tech user who accepts cookies, uses Gmail and has an android phone, google probably knows more about you than even your closest confidante.
I would really love a major news vendor to expose this to the public because I think many people would be shocked to understand this. I don't think many people realize that almost all web pages they visit are connected to the same company that runs their phone (for many) and that provides their mail, and manages all their files, and their work's files, and their online maps, and their internet searches etc etc. They may think they know this, but I don't think they grasp the implications fully.
Icon because we are way way beyond 1984 now.