The app is similar to the one described here - one Activity, several sections accessible from Nav menu toggled by always-visible hamburger or by sliding from left edge.
The sections are very different - say, one showing a list, another: settings, help, logs, etc.
Google's guidelines (here and here) don't seem to provide tips for this exact case, thought frequently I find the interpretation that the back key should switch between the sections.
This is not something I'd expect to happen if we had tabs, and I've thought of the nav drawer to be an equivalent. Is it not so, and if not, what's the justification?