The grenade launchers. How does that work with import? Is that something that can be imported? Since we can are allowed to own them, last I remember.
They can be demilled, or parts kits and then built and registered as F1 DD's in some circumstances. Although most of the 40mm activity in the civvy NFA market is based on American made M203 clones, or 37mm's bored out and rifled to 40mm. In theory you CAN even own/use 40mm HEDP or other explosives it could fire too, but each individual one would be it's own $200 NFA registration tax and form, and you're going to have to conform with Federal/ATF explosives magazine requirements to keep and store them. And in actual practice, none of the producers of such items would sell them to you even if you were going to do all the proper ATF NFA paperwork.
So in reality everyone just shoots flares, smoke, or the .22 LR beehive rounds.
Although in this instance, putting the SIG 553 MG's aside, it's not like you can just import the stuff whole and functional, promise to torch the receivers, and then chase it with the paperwork afterward.
Point of origin being Ghana is weird, but high dollar Swiss stuff from SIG doesn't normally fit the bill for smuggling/terror. I'd bet a few bucks on it being Uncle Sugar/CIA/DoS/DoD getting "sterile stuff" and bouncing it around the world, or some commercial concern that was trying to fulfil a contract for the stuff under those terms for Uncle Sugar, and screwing up or omitting paperwork to keep it on the down-low bit them in the ass. More shady, at least in terms of the laws would be someone like Blackwater/Xe or Dyncorp trying to get some hardware, but that would be unusual, as they have ways of keeping post-'86 MG's offshore on ships etc. or pre-placing it in other countries.