This was apparently a SWAT team that initiated a confrontation in response to a report of a situation involving firearms. Why weren't they already behind cover

This was apparently a SWAT team that initiated a confrontation in response to a report of a situation involving firearms. Why weren't they already behind cover so that if the guy really did come out of the door shooting at them, they were protected? And if they were, why was it necessary to shoot first when the situation obviously wasn't clear at all? Nothing about this adds up.