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 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.