While I'm no fan of that law, it isn't a case of intermediary liability. It's a case of legislators (in a baffling move) deciding that selling 3d printers (and I guess CNC mills?) without vaporware attached should be directly illegal, much like most of the world has decided selling guns should be directly illegal, regardless of how they are used.

It's not illegal to sell these because it would be illegal for the end user to make a gun with them (it might or might not be - but is irrelevant) - it's just illegal to sell them because the legislator said it is.

It’s not the same legal conception of intermediary liability as with online services, but I’d argue that it’s an extension of the same idea. The manufacturer has somehow been conceived as an intermediary between the user and the printed/milled product, and the legislature is attempting to force them to interfere in the manufacturing process, with the threat of liability as a club.

This same trend is happening all over, from banking to communications to manufacturing, where private industry is deputized by force to police consumer behavior, without consumers receiving any of the usual protections provided by the legal process. We’re effectively witnessing the construction of a privately mediated police state.