It is a big deal. If nothing else, it shows that the fanatics are running out of folks so dedicated to the cause that they're willing to die for it.
They were still engaged in terrorist activities and should be regarded as terrorists and murderers, not dupes.
No one has said otherwise. Even if they were dupes, they knew that they were going to kill lots of innocent people -- they're still terrorists and murderers. But if they were also dupes, it's an interesting piece of information in a number of ways.
Interesting to whom? I am not concerned with the whys and what fors when it comes to these pigs. I'm interested in defeating and destroying them.