1. They tried out 40-50 words in Google Trends and backtested all of them. The word 'debt' is the one that performed best over the 7 year period of the study. Does anyone think it's going to be the most profitable over the next 7 years? Similarly I could backtest 50 signals from a random number generator. One of them is going to be the best over the past 7 years, but that tells me nothing about its prospects for the next 7.
2. Eyeballing the graph, about half their return comes from the last quarter of 2008. This tells me (i) the signal just got lucky to be short in a period where the market was tanking, and (ii) they don't have any risk controls. You should never be making 50% of your pnl in a period that represents only 1/30 of your sample. I'm willing to bet that the bootstrap value at risk of this strategy is pretty poor.