I thought it was the same thing until I tried it myself, especially in dark rooms. Having the light from my phone hurt my eyes after reading with an ereader. It’s a really huge difference
But something in your brain works differently when a display doesn't update (e-ink) or updates 24-120 times per second ("normal" display).
Combine that with e-ink lights being a subtle warm glow vs. phone/tablets having MAXIMUM BRIGHTNESS shining at your face...