Many pro players say they do not know when they've hit off of a double bounce. I may only be a 4.0 player but I'll take their word over yours. Now, I don't think Iga is a great sportsperson, but there is zero evidence that she knew it was a double bounce. The ump didn't catch it. Renee Stubbs, who was commenting at courtside, did not catch it and thought Iga reached the ball in time, but of course, all of the online forum commentators who have seen the super slo-mo replay can with righteous indignity condemn all these people in hindsight.
Even if Iga lost that point, it was just taking the game to deuce. With that 6-1, 6-2 scoreline, no way that point was changing the outcome of the match.