I'd say it has more to do with being a male than with being an engineer.
The trait that makes a person a terrorist is more primoral than "engineer type".
Basically, terrorism is a fallback solution to changing/improving the world to fit your needs/desires.
Which is what many male humans and thus male engineers would want to do.
Tech experts are also prone to being smarter than average, narrow minded, misunderstood and socially excluded by people around them.
This in turn leads to frustration. And I'd say roughly 80% of all wars and conflicts go back to simple male sexual frustration. Also terrorism.
Take a smart, outcast male youngster, and, yes, he is indeed very much closer to becoming a leader, innovator, bum, philosopher or, yes, if the circumstances are right, a gun-rampager or terrorist than regular people.
I know that I am closer to being a warrior, leader or bum than a 'regular guy'. There is less of an inbetween for me.
Let's keep in mind, the difference between terrorism and war basically is just the amount of people you kill and the amount of comrades and long-term planning involved.
Looking at terrorism and the technical requirements for effective terrorism, these stats are no real surprise.