The context here is that there are already speculations and some indirect evidence about High-Frequency Traders on the High Frequency band for years (e.g. see [0] from 2018), which made it a naturally candidate. I'm not saying that it's proved, but a candidate worth investigating.

[0] Shortwave Trading | Part I | The West Chicago Tower Mystery

https://sniperinmahwah.wordpress.com/2018/05/07/shortwave-tr...

[1] SHORTWAVE TRADING | PART II | FAQ AND OTHER CHICAGO AREA SITES

https://sniperinmahwah.wordpress.com/2018/06/07/shortwave-tr...

[2] Shortwave Trading | Part III | Fourth Chicago Site, East Coast, Patent, Regulation, and Farmer Kevin Mystery

https://sniperinmahwah.wordpress.com/2018/07/13/shortwave-tr...