The success rate at Google has nothing to do with how many people on HN want to work there, and the artcile provides a pretty confounding factor - that 0.2% success rate includes people applying to interviews for practice. Personally I don't think that many people applying to Google are in that 99.8% because they don't know how to learn during an interivew, it's because their application got scrapped on review stage.
If that was the case then the Google interview would have a 100% success rate, when in reality it is ~0.2%.