I'm surprised by how polished this version of Tetris appears to be, given it's for a word processor with a monitor that doesn't do the art of the game the justice it deserves.
I noticed in some of the screenshots that Tokyo System House (TSH), which produced the game for NEC, sublicensed Tetris from Bullet Proof Software (BPS), which licensed it from Elorg (Электро́норгтехника).
In 1988, BPS produced Tetris for many computer platforms in Japan, including FM-7, MSX2, PC-8800, PC-9800, X1, X68000, and Family Computer (NES). Some of these are NEC products. By 1991, when the word processor version was released, Tetris had been ported to even more machines including TRS-80, Amiga, ZX Spectrum, and Macintosh.
In 1988, BPS produced Tetris for many computer platforms in Japan, including FM-7, MSX2, PC-8800, PC-9800, X1, X68000, and Family Computer (NES). Some of these are NEC products. By 1991, when the word processor version was released, Tetris had been ported to even more machines including TRS-80, Amiga, ZX Spectrum, and Macintosh.
https://en.wikipedia.org/wiki/List_of_Tetris_variants
So I imagine the high polish of the game is due to existing industry experience and references.