The bottom line: if you treat all these cases as one homogenous terrorist thing, you will be very ineffective at intervening in the next one. Yes, they are no doubt being influenced by the social media, ISIS et al propaganda. But at the same time there may be few similarities beyond that.
It really depends on the extent the social media and ISIS propaganda influenced them, in addition to any other underlying conditions.
In case you're keeping score, the Muslims represent 1% of US population, but people "who happen to be Muslim" kill up to 94% of all people killed in terror attacks in the US (not counting the deadliest terror attack of all time). It depends a bit on what you define as a terror attack of course, but the result is clear: the social media and ISIS et.al. propaganda enlarge the problem by at least one order of magnitude and possibly up to two.
So, um ... 90-99% of the problem is one big similarity. What you're discussing are minor variations of the problem.
McHrozni