CUDA is not crap. At the time this paper was written it had been out for a number of years, had good multi-platform support, and had good support for nvidia GPU

CUDA is not crap. At the time this paper was written it had been out for a number of years, had good multi-platform support, and had good support for nvidia GPUs. If they had used opencl they may have been using an immature product, that might really have been apple only at the time (or apple and IBM?). I don't know thie history but 8-9 years ago (when the research work may have started) nvidia was tpushing the cuda idea (almost entirely alone - AMD still playing catchup).