No, not really. Calling something "science-fiction" at the present moment is generally an insult intended to say something along the lines of "You're an idiot for believing this made up children's story could be real, it's like believing in fairies", which is of course a really dumb thing to say because science fiction has a very long history of predicting technological advances (the internet, tanks, video calls, not just phones but flip phones, submarines, television, the lunar landing, credit cards, aircraft, robotics, drones, tablets, bionic limbs, antidepressants) so the idea that because something is in science fiction it is therefore a stupid idea to think it is a real possibility for separate reasons is really, really dumb. It would also be dumb to think something is possible only because it exists in science fiction, like how many people think about faster than light travel, but science fiction is not why people believe AGI is possible.
Basically, there's a huge difference between "I don't think this is a feasible explanation for X event that just happened for specific technical reasons" (good) and "I don't think this is a possible explanation of X event that just happened because it has happened in science fiction stories, so it cannot be true" (dumb).
About nanotechnology specifically, if Drexler from Drexler-Smalley is right then an AGI would probably be able to invent it by definition. If Drexler is right that means it's in principle possible and just a matter of engineering, and an AGI (or a narrow superhuman AI at this task) by definition can do that engineering, with enough time and copies of itself.