They do claim "a revolutionary leap in E-ink monitor refresh speed" and very specifically "37Hz". It seems plausible to me that this is a genuine technical advance.
Best eInk refresh rates are in the several-Hz range, and that with a tremendous degredation in image quality over a full-refresh.
(I've own an Onyx BOOX Max Lumi for 4+ years now, using an eInk Mobius Carta display (2,200 x 1,650 207 ppi). I'm quite happy with it, but I'm also well aware of its display limitations. For reasonably static text it is indeed excellent.)