I disagree with this statement. Behaviour of the program will be determined by machine instructions that the compiler generates for a given source plus the machine environment where these instructions will be run. And it is not guaranteed that the generated instructions will be same for a given source across different architectures and environments that the compiler is run (plus I guess there is generally some degree of non-determinism in the compilers as well, because of the different optimizations it can make under different conditions, which are not "explicit" from the source itself).
As far I understood, in the notion of explicitness that is defined in the article, it is defined that the language where source almost completely specifies the behaviour of program, irrespective of the compiler environments where it is compiled on, is an explicit language.
I think in the sibling comment https://news.ycombinator.com/item?id=16034541 bad_user articulates more clearly the point I was trying to make.