FB Assembly
Looks like an error by the vendor. The fire bottles have two discharge heads, combining the electrical and plumbing connections for one squib each. These are practically identical but have different part numbers to account for different keying of the electrical connector. It appears that the vendor switched them at assembly. Upon installation, the Halon plumbing would be installed by mechanical fit. That is; the head in the Left Engine position on the bottle would be plumed to the left engine and vice versa. The electrical connectors however are keyed, so the Left Engine cable would only fit the discharge head keyed to fit it. Due to the proximity of the heads, it would not take much slack in the cables for the installer to move the electrical connector to the head that it fit on (the one plumbed to the opposite engine).
Now for the blame. At assembly, there should probably be some check for the proper head P/N installation. A visual check of part numbers can be done, but could be overlooked if the Q/A people were in a rush. A continuity test jig could be built (or modified) to fix the proper mating connectors in place physically, making a switch just to get the test passed difficult or impossible.
But the root cause might come down to people doing the assembly and/or installation process not having an understanding of the system. The discharge heads look the same, so what's the big deal? There's enough slack in the cables to get them to fit either side. So we can get the thing installed and check it off the job list. Its the mentality of me doing my little job and going home at quitting time. That and the thinking that everyone else up and down the line got their job done correctly. So why bother looking again?