In the 2nd and 3rd rounds up until the Ruiz knockdown it looked exactly like that was what he was doing. But as soon as he did that he went for the kill against a boxer that wasn't in a position to be put away, and Ruiz probably couldn't have believed his luck and he caught him with a couple of easy big counters. It hurt him bad and as a boxer who isn't used to being in such a precarious position so early he handled it poorly and got decked again. Joshua was wise enough in the 4th in that he did what he should, he kept his distance when he punched and boxed as conservatively as a top boxer should. But then he went dumb again and started going inside and Ruiz had every opportunity to chip away at him in the 5th and 6th, and in the 7th he was a gonner.
Joshua didn't lose due to lacking the ability of a top boxer, he lost due to having the brain of a dunce. His positioning was lacklustre for large parts too.