Well that's just flat-out false. You can print things like frames, receivers, and misc hardware, but you still need machined metal components for parts that need to tolerate heat and pressure, and specialized hardware like springs of specific dimensions and tension which are really not easily home-manufacturable.
The author explicitly links to another article[1] on Tom's Hardware which specifically says this, so, uh, top notch journalism there, fellas.
[1] https://www.tomshardware.com/3d-printing/i-tried-3d-printing...
https://www.vam.ac.uk/articles/the-liberator-the-worlds-firs...
Dig1t•3h ago
https://ctrlpew.com/
Is the best place for guns and guides to building them.