I wondered too and bravely ventured onto the dailymail website when the comments left me hanging. Your hunch was right, the only this i can add is that he walked out

seemingly unaware that they were not matching pairs

There’s an old myth about a shipment of playing cards. The guy buys a whole container of playing cards, but removes the same card from all packs. The shipment is confiscated and later sold for almost nothing because the packs are all incomplete. He then buys the shipment and restores the packs. All this was cheaper than paying import duties.

Maybe this guy is playing a long game.