A special type of threat?

Well, that's intriguing.  I set great store by the market as a strong (though often confusing) signaling mechanism.  From The Stock Market Effects of Islamist versus Non-Islamist Terror by Gan Jin, Md Rafiul Karim, and Günther G. Schulze.  From the Abstract:

We are the first to analyze the effect of terror on stock markets by terror ideology. Surprisingly, we find that Islamist terror attacks created significant negative abnormal returns in American and European markets, but the stock market effects of other terror attacks were almost nil. For our sample of all 124 terrorist attacks in the US and Europe in the period 1994 to 2018 that caused at least five fatalities or ten injured people, we show that Islamist terror attacks are given significantly more air time (also after controlling for attack characteristics and the media pressure of competing news stories). This, however, explains only part of the differential effect of Islamist attacks on the stock markets. 

Could this be interpreted to mean that Islamic terrorism is seen as a systemic threat whereas other acts of terrorism are seen as merely random and not systemically threatening?  

Or perhaps Islamist Terror is serving as a proxy for regional instability, especially with regard to energy markets.