Mamepato would've been different, especially when Iris/Dento were playing the "waiting for attract to hit" game just like Ash was.
It was funny but still those reactions were kind of insulting towards Ash, since it was plainly obvious Ash didn't really know what he was doing when battling Tsutarja (I mean think about it, Mamepato is super effective against Tsutarja and if Ash knew it was a female, why in the world would he not use Mamepato FIRST and FOREMOST, aside from plot saying to reveal all of Ash's Pokemon's Gender). Then again he did tell Pokabu to avoid attract, so its possible either he knew Pokabu's gender, or he assumed all of them were Male.
I would assume then, that Dento made the observation when Ash wanted to use Mamepato for battle instead of Pikachu. Thus Ash came to the realization that Mamepato was female (given its eagerness to battle Tsutarja). However I think that's a big stretch on Dento's hypothetical observation since they Iris and Dento were worried about attract hitting just like Ash was (and if they actually knew Ash they would've assumed he chose Mamepato over Pikachu due to typing rather than Gender, like any "normal" trainer would've done if the games didn't explicitly put genders on the health bar).