Doesn't it say in the article that in the past, 24% of the Hindenburg Omen were followed by a stock market crash? From the article:

Looking back at historical data, the probability of a move greater than 5% to the downside after a confirmed Hindenburg Omen was 77%, and usually takes place within the next forty-days. The probability of a panic sellout was 41% and the probability of a major stock market crash was 24%.

While the past performance is quite compelling, the criteria seem to be extremely arbitrary.