Frankly, their discussion is a bit confusing because they did have optimized versions discussed in the text. And the optimized Scala version did make fundamental changes to the algorithm. They could have kept a better division between the two - idiomatic versus optimized - in both their results and their discussion.

So, jbooth is not accusing them of intellectual dishonesty. And if I consider the following three suppositions: jbooth's understanding of the paper was not complete, your understanding of the paper was not complete, and the people who wrote the paper are smart and hard working; then I simply conclude that performing and writing about this kind of study in a clear manner that will confuse none is very, very hard.