It's not written very clearly, so I can understand the confusion, but that's not how I interpreted the article. It sounds more like the sequence of events went like this:
1) Based on their observations of user behavior, the Gmail team started pushing to simplify Gmail's interface;
2) This prompted a backlash among Googlers, who use Gmail for their work email and therefore need the sort of power-user features that would have been dropped in a simplification;
3) The Gmail team pushed back with a "you are not the user" argument;
4) A giant political furball ensued, with the stakes being whether Gmail would become a simplified email tool for general consumers or a power-user email tool;
5) The "power-user email tool" side lost, but as a peace offering they received a consolation prize: rather than dropping their ideas altogether, the Gmail team would build a separate product (Inbox) incorporating those ideas. (I call it a "consolation prize" because any separate product will have to fight for its own user base, making success much harder than if it could roll out to Gmail's already massive user base.)
Maybe a clearer way to phrase is "they _re_-designed Gmail around people who don't use email".
I.e. the original version of the Gmail was designed by heavy emailers, they then noticed that most users got very few mails and redesigned it (in 2011) for that use-case. (Including the wide line spacing leading to low text-density, and similar things that lots of people complained about at the time).
1) Based on their observations of user behavior, the Gmail team started pushing to simplify Gmail's interface;
2) This prompted a backlash among Googlers, who use Gmail for their work email and therefore need the sort of power-user features that would have been dropped in a simplification;
3) The Gmail team pushed back with a "you are not the user" argument;
4) A giant political furball ensued, with the stakes being whether Gmail would become a simplified email tool for general consumers or a power-user email tool;
5) The "power-user email tool" side lost, but as a peace offering they received a consolation prize: rather than dropping their ideas altogether, the Gmail team would build a separate product (Inbox) incorporating those ideas. (I call it a "consolation prize" because any separate product will have to fight for its own user base, making success much harder than if it could roll out to Gmail's already massive user base.)