Well, they’re terrorists, definitely, whoever is behind it. But their identity is not entirely clear. The guy doesn’t look Muslim, and in fact looks more like a leftist - he also didn’t blow himself up but just left the backpack to detonate by itself, which would be more typical of a Marxist than a Muslim.
In the photo, he also seems to be wearing bands around his forearms. Does this mean anything in anbody’s religion?
History is spattered with the blood left by victims of marxist and anarchist terrorists who had no religion.