it's definitely fake. the screen can only turn on and off the individual lines of the LCD for the numbers - it can't make blocks. that would require a high resolution like that on a ti-89 or even and 83. no 8 digit can ever do this unless you like stacking lines to form "8's" lol
plus, even if it didn't turn into blocks halfway into the video, when it says "TETRIS" the display uses a slightly different type of layout.
The top and bottom lines are split into two individual LCD lines rather than one. i.e. the number 8 would be made up of 7 LCD lines on the starting display and 9 or 10 on the new "TETRIS" display.
FAKE.
now as far as ti-89 games, yeah they are NICE compared to any other calculator. I have a 3-d wire-frame space game, knockoff of starwars. it's pretty neat but really pushes the limits of the processor. whole up/down/left/right 3-d playing field too just like a computer flight sim but without gravity of course.
if you know how to reliably overclock your calculator it would run nicer, but i never cared to that extent nor do i want to overheat my 100 dollar calculator i that need for calculus. tetris is good enough anyway. tanker is good too. and mario. blah blah blah...