After looking closely to the 767 in today's events I see 2 slide deployed on the right and the front left deployed. In after action pictures the left rear door is not open so I do not think there was a slide failure.

To me it looks like they chose to open just the 3 based off of fire size wind, ect for the safest potential routes of egress for passengers. Just my thoughts NTSB will be the deciding factor here on what really happened.