Click on your profile picture at the upper right corner then from the dropdown menu click on your own nickname, a new tab will open. From there click on “Preferences” and from that new window go to “Blizzard Account Management” and go to “Privacy” section and scroll down. There it reads:
GAME DATA AND PROFILE PRIVACY
Share my game data with community developers
Blizzard allows external developers to build applications and experiences for our players using game data. Unless you turn this share off, some information associated with your Blizzard account, such as gameplay data and your BattleTag, may be shared with external developers. Your name, email address, physical address, telephone number and other similar information will not be shared without your specific consent.
They don’t need telemarketers, it’s about “applications” as far as I can tell; external partners can be social media as much as mobile and an addon for the game. Your habits and actions at the online play are a market opportunity.