No biological process is 100% precise. DNA copying being imperfect is the driver of evolution, which is the prime example of this. What I assume they're referring to is that their ribosomes just "make fewer mistakes" when creating proteins from mRNA.

These "mistranslated proteins" are normally infrequent and benign, and their material is recycled eventually. But that whole process wastes energy, so making a "better ribosome" makes all cellular processes more energy efficient and allows the energy budget to be reallocated.