Another frustrating design choice by Msft that drives users nuts. If you link to a document using the "real" url (ie /documents/file.docx), it doesn't open in the browser app - regardless of how you configure file opening settings. You have to waste time grabbing the wopiframe url from the file itself which takes several clicks to find.
This is just a stupid design - there's no other way to describe it. But if it has to be this way, then Msft MUST provide some visual clues so users don't think it's a bug. I'm sick of making excuses for Msft's amateurish design/development practices.