Joshua's seventh-round stoppage by Ruiz came as a huge surprise as his opponent had been given barely one month's notice for the fight and weighed in at over 20 pounds heavier than the Briton.
"When a man doesn't want to be there once, he will always do it and it's hard to come back from", the self-styled "Gypsy King" said on Wednesday.
The 40-year-old said that after the fight Joshua told him that his "senses weren't there" after receiving a blow to the side of his head.
"Ask any top trainer who has been around the sport a lifetime".
Wilder vs. Fury 2 is tentatively scheduled for 2020 while Joshua will rematch Ruiz Jr before the end of the year, after his promoter Eddie Hearn triggered the contracted rematch clause. However, Joshua is open to coming back to Madison Square Garden in NY.
"If they [Team Joshua] want me to go over there [the UK] they've got to give me 50 million dollars".
Rivals Tyson Fury and Deontay Wilder tweeted highly different statements towards Joshua following his loss.
The Briton, whose fight with Schwarz is the first of a multi-fight broadcast deal agreed with ESPN in February, is the only boxer Wilder has faced and not defeated.
Speaking of Love Island, he said: "Well, it's not something I can say I watch ever".
"They thought I'd be half the man".
That was after the pair battled to a draw in December in Los Angeles. What were people seeing?
"People who don't understand boxing look at a fat man and think he can't fight".
But unbeaten Fury, who shed around 10 stone (64 kilograms) in a bid to re-establish himself in the heavyweight division after a battle with mental health and drugs issues, said body shape was no indicator of success.