10 MB is not too bad for a GUI app. If the app is full screen, display is FullHD and has 8 bit depth, that's almost 8 MB memory for the back buffer alone. Enable HDR and pixels become 8 bytes RGBA16_Float instead of 4 bytes BGRA8_Unorm, twice as much memory.

2 bit 160x144px ought to be enough for anything

This is only relevant if we assume CPU rendering. The article described system RAM use, not video RAM use. Task Manager doesn't combine the two.

They clearly spent it on maintaining their independent Chromium instance instead.