Yeah, it mentions this at the end of the article:

But here's the rub: That tangy paste served up at nearly all sushi bars — even the ones in Japan — is almost certainly an impostor. Far more common than the real thing is a convincing fraud, usually made of ordinary white horseradish, dyed green.

Native to Japan, wasabi is notoriously difficult to cultivate. The plant takes nearly two years to reach maturity and requires exacting temperature, shade, gravel and water conditions. It can cost more per pound than even the choice tuna it sits on.

Genuine wasabi must be consumed fresh, with the stubbly rhizome, or stem of the plant, grated tableside just before eating. On the plus side, just a small dab offers the same benefits as the capsule supplements used in the Tohoku study, or 0.8 milligrams of 6-MSITC.