Michael Griffin took charge of the bout between the two heavyweights back in June, where Ruiz Jr recorded a seventh-round knockout win.
Joshua had gone into the fight as the overwhelming favourite, having been unbeaten in his 22 previous contests.
But despite flooring Ruiz Jr in the third round, he was sent to the canvas three times throughout the match before Griffin put a stop to it.
Criticism was levied at Joshua by punters after the match who claimed the 30-year-old had given up.
But Griffin refuted those suggestions.
“He wasn’t quitting, he’s looking for more time,” he said. “I don’t think in any sense he was quitting the fight, he just wanted those seconds.
“But the rules don’t allow me to give him those seconds.”
Joshua had looked dazed for much of the fight, after Ruiz Jr caught him with a hammer blow to immediately return his third-round knockdown.
He struggled to remain steady on his feet thereafter, and later complained to his corner, asking: “Why am I feeling like this?”
At the time of the stoppage, two of the judges had Ruiz Jr in the lead on their scorecards by just a point, while the third judge had the fight in favour of Joshua.
The pair are now set to rematch in Saudi Arabia on December 7, where Joshua will look to regain his WBA, WBO and IBF world heavyweight titles.
“I’ve learned a lot of things from the defeat,” Joshua said. “I’ve learned to take a loss like a man, and to be thankful that I have a second opportunity to go again.
“I don’t like to talk about it too much because the thing that goes on the record is the loss, not the description. It definitely had an effect on me, but it takes more than that to knock a man like me back.”