All I can do is speculate. The homeowner had already exhibited pretty unstable and hostile behavior. Also, a police officer was dead and it wasn't clear where the shot came from. That situation tends to cause police officials to assume the worst per the adversary.
Once all the information came out the homeowner was cleared and released. Again I will say if the homeowner had not behaved in such a strange and hostile manner initially there would never have been any actual confrontation with the SWAT team.