Even though the mud may not be from the ocean but it may (or may not) be the mud that help the system to succeed. Most articles about this mud, suggested that the minerals in the mud could have help the growth of the macro algae and thus increase the nutrient export. It's like adding additive in a solid form and in a time released manner. By glorifying the description of the mud, the seller can (probably) hike up the selling price. I think hobbyists can manually add the minerals for the macro but that may become a burden and finally give up. It's proven iron increases the growth of macro, but how many of us do add that? I did not.
I used miricle mud in one old system that came along with it, the plants(macro with roots) growth with the mud is faster than the plants on the sand in the same eco filter. The idea is like freshwater planted tank, growth of the plants are better where they were stuck to the proper substrate while they grow slower in pebbles in the same tank. I always use this trick to reduce the amount of work to trim my plants while staying in shape. Worth the mony is another issue.
A reverse thinking here. One of the famous fertilier for land plants come from ponds not from the ground-the pond mud. So the original of the product does not matter, it's the results that matters.