The numbers given in the article specifically are users not paying customers. As quoted:
> Google's G Suite boss Javier Soltero... did not say how many of those 2 billion users were paid
Additionally it indicates that Office may have more paying users:
> Google said roughly one year ago that 5 million businesses are now paying for G Suite, which pales in comparison to Microsoft Office 365's 200 million monthly active users of its version for businesses.
Likewise, there is no free tier of Office/Microsoft 365, but there are free services that are considered part of this suite. How many of the 200 million monthly active users are customers? How many users were paid? If a person uses the free tier of OneDrive, OneNote, or Skype they are not considered a customer even though they are an active user.
When you compare, you do like for like. The comparison is GSuite to Office 365, and many independent studies have said Google has a larger market share.
However people take what is free for granted and don’t consider it a part of the market. For instance, many hold that iOS is a monopoly despite being a minority of the market because you pay Apple for it, where as Android is just free and Google does not get your money for its use.