It's a fair bet that quite a few or even all of the attackers (but let's stick with probably some) share the Islamic religion. But that does not mean that Islam per se has anything to do with it, what it points to is that religion is a tool that can be used to subvert people into committing acts that they would otherwise likely not engage in, especially when they're young, impressionable, stupid or all of the above.

So even if Islam is nominally involved and even if the fact that religious people have a fringe element (like all people!) that does not mean Islam is the cause of this. Just like Catholicism is not a religion centered around pederasty and just like atheists don't generally go around shooting people.

I guess it's the style of attack that makes you think Islam. On the other hand if 150 innocents get killed by drones you think USA and by tanks and artillery you might guess Russia or Israel. I'm not a fan of any of the above.