Reference to this can’t be found in any history books.
Well that part ain’t correct. I think maybe they mean high-school history texts?
Just a few examples of not school texts but books on history, from Amazon. I stopped at 5:
https://www.amazon.com/s?k=tulsa+race+riot+1921&i=stripbooks&crid=3BF2MDAKF0HB6&sprefix=Tulsa+%2Caps%2C173&ref=nb_sb_ss_i_1_6
Tulsa 1921: Reporting a Massacre
by Randy Krehbiel, Kevin Meyer, et al.
The Burning: Massacre, Destruction, and the Tulsa Race Riot of 1921
by Tim Madigan, Bill Andrew Quinn, et al.
Death in a Promised Land: The Tulsa Race Riot of 1921
by Scott Ellsworth and John Hope Franklin
Riot and Remembrance: America’s Worst Race Riot and Its Legacy
by James S. Hirsch
Reconstructing the Dreamland: The Tulsa Riot of 1921
by Alfred L. Brophy