Are there any examples where the film does give the origins of the zombies? What are the similarities between 28 days and return of the living dead with regards to their providing a back story? Do they explain anything or just gloss over the improbable enough to get things rolling?
I like your suggestions for providing back story. The chemicals is a classic format for explaining the situation. This plays on peoples ignorance of chemistry...maybe there are chemicals that can do this. I suspect the audience are going to be less inclined to accept that music would have this affect. There is a lot of research of literature on how music affects people so it might be good to have a look into that area further and armed with that knowledge, how successful this genre was with the music we were given. This will further allow you to come up with a more suitable proposal for your version of the music video...in theory.
On a slightly similar subject, there are a few popular science books by people like Michael Shermer which focus on the subject of why people believe the stuff they do. This might offer up some suggestions for how to best sell a narrative. What is it people need for a story to survive?
The setting is surely only superficially different from Romero? The premise is the same at the core. A small cluster of people trapped with no obvious escape route. The classic zombie films of the past had other limiting factors such as budget and resources.
Would the zombie genre work without this elements of being trapped?
You claim that zombie films typically have an antagonist whose ultimately responsible for the failure to survive. How does this claim fit in with Negrita? Does it fit, if not, how does this affect the story?
What is the significance of your observations that zombies through the decades have gotten quicker? What production benefit is there for slow moving zombies which might have contributed to that being a choice for zombie flicks in the 70's?
Compare this to other films which play with the fear reaction of the audience. Is it merely a creative decision to have zombies feel like a slow moving unstoppable force? Like 'The Blob'. How do they get round the relatively slow speed of the spiders in 'arachnaphobia'? If zombies are slow and stupid, how are they scary?