If the home can't meet his care needs, he will be reassessed and moved to a more suitable environment. I would think they have checked for things like infection etc if he's exhibited aggressive type behaviour before - it's not always the reason, but it can be.
Social worker should have input as well as mental health team about the type of environment that would be appropriate for the type of behaviour or issues your father is showing, to make sure he's getting his needs met - that can be part of the issue with aggression, that the person isn't having their needs met by their current environment and they become aggressive. It's not a failure on anyone's part, things can develop quickly. It can also be that some people just don't get on, people in care homes haven't chosen the people they live with, and not everyone can get on well together, and unfortunately with Alzheimer's or dementia, the inhibition that would generally stop us lashing out someone else has deteriorated.
It may be that he needs a specialist dementia unit, staffed with mental health nurses rather than a care assistant led home, or a nursing home which is usually general nurse led.
Have you spoken to the home about how the land lies and what they are thinking? And what type of home is it? In practice, there usually needs to be a bit of 'evidence' for reassessment, such as records of repeated challenging behaviour, or for the incident to have been very dangerous, before anything happens fast.