The trick used there is exploiting that if you export something to have it undergo modifications abroad and then subsequently re-import it, the import rules are different and you typically do not pay the normal tariffs.
Now, in Norway we don't have a lot of tariffs in general, but we do have some significant ones on food and such, including cured hams, to protect local producers.
So, someone clever figured out how to exploit this. Buy a suitable pig carcass in Spain, transport it to Norway and import it as a whole pig carcass which has a low tariff, then have the trucks do a U-turn right across the border and drive back to Spain, unopened. Only fresh fish have export tariffs here in Norway, so nothing to pay there.
Back in Spain you have the pig get processed into your Serrano or Iberico cured ham[2], and then transport it back to Norway. When it comes back you point to the original import declaration and claim the cured ham is a modified pig, and thus not pay the tariff for cured hams.