Almost none of these guys are officially connected to ISIS, just inspired or motivated by them. It's just that ISIS is happy enough to claim responsibility any time 'allah ackbar' is shouted in combination with murder.
I'll be interested to see what the official story out of Germany turns out to be, they've been weirdly eager to put on a contortionist act whitewashing other situations, even at the expense of their own citizens, but a shooting's a little harder to throw a dustcover over and push off into a corner.