It's most likely a bug. Some dev added tracking to all the href's and just didn't think about phone numbers.
The title of the article sounds like they did it on purpose, which i doubt.
With a typical bug code works not as author intended it to work. Numbers of such bugs can be reduced by testing and better tooling. But software development as an industry creates incentive to be overconfident and not to question own assumptions: developers who don't stop to read documentation/standards/gather information in anther way deliver more features in less time.