Perhaps FDM 3D printing does emit nanoparticles during the process of printing, but the syllogism does not prove it or even suggest it.
Parenthetically, your headline is not actually addressed by the body of your question. As an answerer, I have been misled by other questions which seemed clear enough from the headline, but where the question body actually posed a completely different question.
Double parenthetically, your final question does align with your headline. The discussion of 3D printing and the assertion that it is dangerous is not actually relevant to the question at all. It might be better to remove the references to 3D printing and post this in another SE group focused on human health.
The first point, that breaking down or melting plastic produces nano-particles is not supported by your reference. The reference refers to the mechanical breakdown of particles in a simulated oceanic environment and does not mention melting. The reference is silent on the possibility of melting producing and emitting nanoparticles.
In an FDM 3D printer, the melting takes place in an enclosed capsule, the hot-end. The plastic is heated to the point where the viscosity is low enough that the pressure of the unsoftened plastic filament pushes the softened material out of the hot-end through the nozzle. Upon exiting the nozzle the temperature falls, and the plastic begins to recrystallize.
I have seen no evidence of outgassing during printing with dry filament, other than an odor. Usually melting joins separated objects, pellets, and larger particles in a unified liquid state.
Without specific testing, one can not say there is no risk of nanoparticles emitted by FDM 3D printing. Ventilation remains a useful method of reducing local exposure to nanoparticles and odors. Airborne risks are one of the many risks to be considered, but I have no evidence that they are more serious than the burn risk, the fire risk, or the risk of a stroke from high blood pressure induced by failed prints.