Oakland juries are not known for brainpower. That being said I agree 100% with your analysis. The jury probably felt it was unfair to lay 100% of the blame on these numskulls when many others (city, landlord, Oakland PD and fire) were negligent. Personally I see no loss to society from imprisoning these clowns until they are senior but maybe cheaper just to kick them loose and let them OD within a year.
That alone might have raised sufficient doubt as to Mr. Harris' culpability since he was at the event himself, and apparently attempted to help some people escape.
Clearly the lack of oversight by the city inspectors allowed a dangerous situation to exist, but the attendees also should have been able to assess the dangerousness of the situation. One of the points many news reports have made is that the building lacked fire exits or fire exit signs.
That alone should indicate to visitors that the building is a dangerous place. One look at the interior would have also told them that. Every adult of normal intelligence should have been taught as a child to look for exits, have a plan to escape a fire, etc.
The blame can't entirely be laid at the feet of the defendants, even though they made a convenient target for the government and others.