Software has economies of scale in distribution. In fact the economies of scale of software are the key point of how software businesses are causing disruption. A single software program can be replicated infinitely at zero cost and allow anybody who has 1 liter of milk to have 1000 liters of milk at no additional cost. So in the author's example, software would be the same price for both 1 and 2 liters.
Complexity is something completely different and is well known in all products. I can design a calculator that adds numbers very easily. A calculator that does fractions is much harder to design and costs more. A car with a more complicated engine is much harder to build than a simple engine. This has nothing to do with the actual economies of scale of the calculator or car or you could say that cars have dis-economies of scale too - and obviously they don't. They're the poster child for economies of scale.
Building a truck that is 10km long is worse than building 100 trucks that are each 100m long, but this has nothing to do with 'diseconomies of scale' inherent in trucks.
Complexity is something completely different and is well known in all products. I can design a calculator that adds numbers very easily. A calculator that does fractions is much harder to design and costs more. A car with a more complicated engine is much harder to build than a simple engine. This has nothing to do with the actual economies of scale of the calculator or car or you could say that cars have dis-economies of scale too - and obviously they don't. They're the poster child for economies of scale.
Building a truck that is 10km long is worse than building 100 trucks that are each 100m long, but this has nothing to do with 'diseconomies of scale' inherent in trucks.