That still doesn't mean it's not plated. I'll reserve my judgement until they actually produce it and it comes with an actual certificate to prove that it's 18k gold rather than just plated.
From the marketing speak on their website, it sounds as if they have mixed the gold with something else to make it stronger. Which, normally would not qualify it for 18k anymore. So it's either they've mixed it with something stronger or they've just plated a harder alloy in 18k.
After all, plating is just depositing a thin layer of gold, or silver, onto a much harder metal.