I looked at the data last time someone posted it, and the article cites facts only as convenient to their viewpoint.
I think the FBI definition of terrorism is a fair, and accurate one. Unfortunately, two major events skew the statistics badly; 9/11 and Waco. The Branch Davidians can hardly be blamed for being murdered at the hands of the ATF, and 9/11 was a freak incident.
Under their definition, ecoterrorists are treated as terrorists, and when you compile the statistics, they do perform a lot of damage, in many separate incidents. They just don't kill that many people on purpose. When you factor in incidents where people were intentionally killed in terrorist incidents, minus 9/11, you would get a fair idea of the "level of danger" you would get from Muslim terrorists.
The article, by the way, is crap. They omit clear instances of terrorism, like the guy killed at the El Al ticket counter at LAX a few years back, and use fucktarded logic in making their graphs. In one graph, they randomly mix ethnic groups, with religions to make some point. That point is unclear because their data sucks.