SketchUp probably does not have the intention to access any secrets in Chrome.
But SketchUp embeds its own browser engine (a “copy” of Chrome, to be more precise CEF) for displaying 3D Warehouse and many extensions. It could be possible that CEF shares its preferences location with any other installation of Chrome. By accessing the same user preferences that you use in Chrome, CEF would also have your login details available whenever you want to login to a website inside SketchUp’s embedded browser.