As others have noted, its the "modern display" that does it.
From the wiki here:
"Display: 8 lines, 40 characters LCD, twisted nematic (gray) monochrome, with 240 by 64 pixel addressable graphics. The screen is reflective, not backlit.[3] The screen was made by Sharp Electronics.[4] The LCD controllers are by Hitachi: (10) HD44102CH column controller ICs and (2) HD44103CH row driver ICs; the HD44102CH's provide the programmable hardware interface to software. The refresh rate is about 70 Hz (coarsely regulated by an RC oscillator, not a crystal)."
Not really. Fundamentally things like this are driven by physics, not engineering or cleverness.
We've had solar powered calculators with LCD displays for decades. We're not really going to get much lower power without changing Fundamental technologies at the material and physics level. Much of what we have material and physics wise "is what it is", on this planet anyway.
From the wiki here:
"Display: 8 lines, 40 characters LCD, twisted nematic (gray) monochrome, with 240 by 64 pixel addressable graphics. The screen is reflective, not backlit.[3] The screen was made by Sharp Electronics.[4] The LCD controllers are by Hitachi: (10) HD44102CH column controller ICs and (2) HD44103CH row driver ICs; the HD44102CH's provide the programmable hardware interface to software. The refresh rate is about 70 Hz (coarsely regulated by an RC oscillator, not a crystal)."
It's not even backlit.