Science

Here's the study, for anyone who wants to read it. It's surprisingly short and open access.
A few things:
The participants took Wasabi supplements once a day for 12 weeks, not just normal Wasabi. In each pill, there was 0.8 mg of the active compound (6-MSITC). Quick googling gave me the following for the level of that compound in actual Wasabi:

Another study determined ~550-556 μg/g of 6-MSITC in wet weight of wasabi root [10] . The present study observed a concentration of 120-150 μg/g wet weight of 6-MSITC in stem and rhizome blend.

In other words, you could actually also get the same amount of 6-MSITC that was in the supplements by eating a few grams of regular wasabi each day, assuming that the processed stuff still has similar levels. The abstract provides a reasonable summary of the study, and of the fact that it agrees largely with some previous science on the subject (although there's not a lot, two studies in small journals):

Cognitive functions decline with age. Declined cognitive functions negatively affect daily behaviors. Previous studies showed the positive effect of spices and herbs on cognition. In this study, we investigated the positive impact of wasabi, which is a traditional Japanese spice, on cognitive functions. The main bioactive compound of wasabi is 6-MSITC (6 methylsulfinyl hexyl isothiocyanate), which has anti-oxidant and anti-inflammatory functions. Anti-oxidants and anti-inflammatories have an important role in cognitive health. Therefore, 6-MSITC is expected to have positive effects on cognitive function. Previous studies showed the beneficial effects on cognitive functions in middle-aged adults. However, it is unclear that 6-MSITC has a positive effect on cognitive functions in healthy older adults aged 60 years and over. Here, we investigated whether 12 weeks’ 6-MSITC intervention enhances cognitive performance in older adults using a double-blinded randomized controlled trial (RCT). Methods: Seventy-two older adults were randomly assigned to 6-MSITC or placebo groups. Participants were asked to take a supplement (6-MSITC or a placebo) for 12 weeks. We checked a wide range of cognitive performances (e.g., executive function, episodic memory, processing speed, working memory, and attention) at the pre- and post-intervention periods. Results: The 6-MSITC group showed a significant improvement in working and episodic memory performances compared to the placebo group. However, we did not find any significant improvements in other cognitive domains. Discussion: This study firstly demonstrates scientific evidence that 6-MSITC may enhance working memory and episodic memory in older adults. We discuss the potential mechanism for improving cognitive functions after 6-MSITC intake.

They tested the study participants once before and once after the 12 weeks of daily wasabi supplements. The participants were not tested for any long term cognitive effects.

As someone else has pointed out here in the comments, the study does list a Wasabi company as one of the sources of funding:

Funding
This study was founded[sic] by KINJIRUSHI Co., Ltd. and the Japan Society for the Promotion of Science (19H01760, 22H01088).
Conflicts of Interest
This study was supported by KINJIRUSHI Co., Ltd. The funding body had no role in the design of the study, collection, analyses, or interpretation of the data, writing of the manuscript, or the decision to publish the results.

Also, I don't want to poison the well too much, but I feel like I should mention that the editorial board of the journal resigned in 2018 because the publishers "pressured them to accept manuscripts of mediocre quality and importance". Doesn't mean it's all bad, but it's a very early study and more research should be done.