BroJoeK really is stretching to try to include those two deaths as part of the battle. Other than that his commentary has been pretty reasonable.
Most accounts of the battle will tell you that the sole battle casualty was the Union horse.
These other deaths were the result of an accident while firing a salute.
Sure, a salute in the surrender ceremony forced by Confederate military actions.
They were just as certainly casualties of war as were, for example, Hawaiian civilians killed during the Japanese attack by US projectiles fired at Japanese bombers.
In both cases, enemy actions were the root cause of those deaths.