Nothing about having a private office precludes seeing coworkers. In the heady days of my long-lost youth when I still had an office, I stepped outside of it when I wanted to see my coworkers and went back inside and locked the door when I didn't.
And you were likely much less efficient because of less interaction with your more knowledgeable colleagues. You don't know what you don't know.
Efficiency is an attribute of doing the work. If you're always interacting then you're never doing the work; neither efficiency nor inefficiency can exist at all.