Mojave screen saver starts randomly

I have a new Mojave (10.14.1) installation on an iMac (Retina 5K, 27-inch, 2017). My screen saver is set to start after 5 minutes. I have a hot corner defined to start the screen saver.

I have noticed that periodically, the screen saver just starts up out of the blue. Typically this happens while I am scrolling with the magic mouse. I am definitely not hitting the hot corner.

Any suggestions for why this is happening and how to stop it?

Does Android 7 “Data Saver” also applies to metered WLAN?

The section ‘Use Android Nougat’s “Data Saver” (Android 7.0+)’ under this site ‘How to Restrict Background Data for Metered Wi-Fi Networks on Android’ mention:

Android 7.0 Nougat introduced a much more granular way to take the reins on your mobile data with a new feature called Data Saver.

Basically, this allows you to limit background data used by apps, but whitelist anything that want to have unrestricted access. This means background data is disabled for every app by default, then you can pick and choose where to grant unlimited access

And that’s all there is to it. It’s worth keeping in mind that this only applies to mobile data-all apps will remain unrestricted while on Wi-Fi.

My question is whether this ‘Data Saver’ option applies to Wi-Fi that you set to metered, meaning metered WLAN?