Ehh, i don't know what to say, because i believe that Booster is the bad guy, and i am working on the theory about it. So he could say that Quote is a robot only because he didn't want Sue, Kazuma and himself go to the sandzone, very dangerous place, as he said. He just thought 'hey, i don't want to go there, so meyba i could say that he is a robot, he isn't even saying anything, so he won't disagree, and then i could say that robots are immune to many things and hard at all, and he would go to the sand zone in our place!'
So yeah that's what i think, but!
I can't say that they aren't robots, because when you're saving curly in waterway, you are reading draining water instruction for ROBOTS, and it is working. Also, Curly seems to remember their mission as robots after eating the mushroom. So i think that they are robots actually.