This type of engine would look just as clean with any type of good oil that has effective detergent additives, there is nothing special about Amsoil. The filter change interval seems a bit short, but I don't know what that decision was based on.
I don't pay any attention to the Amsoil hype because their tests are not realistic in engine wear terms and they fail to compare with some of the better oil types available. You could getter better results in most of their tests by using a can of Moly or Zinc compound, but if you ran a real engine on pure additives it would cause some real problems.
The tests they use were probably chosen because their oil would produce better results, if they were really interested in proving to intelligent users that they made the best oil, rather than had the best marketing team, they would run their oil in a big fleet of diesel trucks and taxis and then show the UOA's for the different oils used.
When realistic oil tests have been done in the distant past it showed that there was not much of a difference in engine wear factors between all the brands and that viscosity, oil filter quality and change intervals were more important. Most of those results were binned as a result, as they were sponsored tests and the oil company was not interested in publishing results that said their oil was no better than the others.
Genuine full synthetics like the Liqui Moly Synthoil I use, or the Amsoil products are slightly better if you do a lot of stop start driving in winter, but that is about it and for many users a good quality major brand dino or part synthetic will be just as good, unless you are pushing the boundaries of the oil change interval limits and that is a dodgy thing to do if you suffer from unexpected fuel or coolant contamination with any type of oil.
One final point is if you are trying to compare UOA results to figure out the best oil to use, it helps to check what type of use the engine is subject to and if it was during summer or winter etc. There is not much point comparing the results for an engine in a long distance truck during the summer with those from a delivery truck during the winter. I am currently trying to figure out if Diesel Synthoil 5/40 is better than Synthoil High Tech 5/40, but I will wait until the winter period to do a UOA otherwise the results would be meaningless.