Same screen specs but ADB reports different pixel density depending on OS version (LDPI/MDPI)

Question

I suspect that later versions of Android OS are forcing MDPI rather than using LDPI. It would be helpful if someone could point me toward info/technical terminology on the exact change in the OS.

I have 2 devices with the same screen resolution and screen size, and the device models are nearly identical. It's a smaller, kind of obscure manufacturer, though that's probably irrelevant. One device is Android 6.0 and one is 8.1. Calculating pixel density from resolution and screen size, real-world pixel density should be about 141 pixels/inch, which would fall in the Android classification of LDPI.

The older OS seems to use LDPI and the newer one seems to use MDPI. This is based on observation and calling adb shell wm density.

Can anyone point me toward what changed in the OS? Thanks!