Looks like a sharp memory lcd to me. From google image search:
They use variations of polymer stabilized liquid crystals such as PNLC (Polymer Network Liquid Crystal), which all have in common that they are in a stabilized gel-like form, allowing for a greatly reduced power consumption to keep the electrical field for the orientation of the polarizing elements active. Variants have been described (though I am not sure if this applies to sharp ones in particular) that only consume significant power for black pixels (and of course any switching).
In small sizes like those, you only need microamps to keep the image stable, which makes them suitable in energy harvesting environments.
However this all comes at a drawback: Most versions are only available in black/white (instead of grayscale), and the switch rate is in the order of visibly many milliseconds (although at least in the lab there have been improvements).
Unfortunatley the last time I tried searching for them, the mirror background ones were not available, at least in quantities. Hopefully this has changed...