Why do you think Douglass says of the killing of slave Demby ‘in an instant poor Demby was no more. His mangled body sank out of sight, and blood and brains marked the water where he stood.”?

To me it seem as if hes sayint how he died instantly but idk i need more!!!
HELP PLEASE!!

According to a reading of the full text, Denby was shot in the head at close range by a musket while standing in a creek trying to escape a whipping at the hands of Mr. Gore. A sudden and messy death would be expected. As the creek was deep, his body disappeared.