that chap is also a grade A asshat.
You dont need to buy a "printer", just send the CAD off to a company that uses them. They would have to be pretty tuned in to figure out what the bits are for. I could have that assembled on my desk in 24 hours should I wish, and I would guess at a cost of around £500. Based on ordering parts from different suppliers to avoid suspicion.
Of course there are other cheaper and probably better ways to make a firearm, the devastating thing about guns is they are fundamentally simple. I am however irked at the coverage of the technology (which is fantastic) being all about nutjobs making plastic guns.
I use this type of tech on a weekly basis, it has transformed the engineering/prototyping world and it will go on to transform manufacturing. I have seen this type technology used to recreate from scan data, in titanium the facial bones of a motorcycle crash patient, and effectively be directly implanted into the patient rebuilding his severely smashed up face. Similar tech is also used in to build the skeleton around which the first artificial lab grown organs to be transplanted into humans have been grown. There are so many amazing things being done it is perhaps inevitable you end up with people like these selling the darker possibilities.
It is worth saying that this sort of additive modelling has been commercially available for at least a decade. But it has developed fast and the prices are dropping rapidly.