540A current spec came from the FET's spec @25°C trans.temp. 180Ax3=540A.
The 180A is listed in IR's IRF6691 datasheet, which was employed in earlier batches of Novak's GTB ESC, but later GTB switched to STK850 which did not mention this spec in its datasheet but Novak continued using it.
It's good Novak didn't quote this spec in red circle, they can improve the ESC performance to 260*3= 780A ESC simply by this.
I have to agree with lutach, a 90A rating for this small ESC would make Novak look more realistic and of a down-to-earth flavor, at least to those who know what the ratings are talking about.