This headline from an article in BigThink grabbed my attention. The article doesn't dive into how the food is actually made, but this interview with the founder fills in the gaps:
The idea seems to be to do a highly efficient type of photosynthesis: Instead of growing multi-cellular plants in farms as we do now, Solar Foods plans to grow bacteria in an industrial environment. The result is food produced using very little energy and water.
One immediate application I can see for this is as feed for farm animals, supplemented with fat (as Soylein has none), and the necessary micro-nutrients.