The main difference between the two is that the ISS vegetables have more microorganisms, but that's probably just because of the microflora that live on the space station. None of them, however, are harmful to humans, such as E. coli and Salmonella. The scientists' findings are significant, because they tell us that we can grow food in space for long journeys. NASA regularly sends supplies to the ISS, so the station's crew isn't at risk of food shortages. For trips to the moon and Mars in the future, though, NASA needs to find a way to supplement pre-packaged food.
Massa and Khodadad explained:
"Right now we cannot guarantee that we will have a diet to meet the needs of the crew for these longer, deep space missions, so one potential solution will be to supplement the packaged diet with fresh produce. This [space-grown lettuce] will provide additional vitamins and other nutrients, flavors, textures and variety to the packaged diet. Growing plants may also help with menu fatigue and provide psychological benefits when astronauts are far from home. In the long term, if we ever want to have space colonization, growth of crops will be crucial for establishing any level of sustainability and self-sufficiency.
In addition to providing food, plants may also play a role in future Life Support Systems needed for long-duration missions. Plants generate oxygen as well as remove and fix carbon dioxide, which is critical in closed systems like the ISS or future moon/Mars facilities."
Since humans can't live on lettuce alone, NASA also sent kale and cabbage to the ISS to figure out if astronauts can grow them for long trips in the future.