That popup is standard for any app that is approved to potentially use location in background and you don't use often. I think it's meant to discourage apps to ask location in background altogether
I think the pop-up is telling me it was using my GPS, especially since the GPS icon on the Settings page where you can retract the permissions was lit up to indicate "Recently used".
I don't want to jump to conspiracy theories but the experience scared me a bit because it was around the exact same time of day I had grabbed an Uber to go to work the last time I had used it.
Perhaps it was an errant random notification meant to scare me, perhaps it was a late delivered push notification opening Uber in the background, perhaps it was Uber seeing if I was home and wanted to commute to work again.
Uber would like to access your location at all times
[Yes, allow in the background]
[Yes, only when open]
[No, deny all together]