What is ironic about the description, "thick blood welled out of him like red velvet ... "?

The irony lies in this luxurious and illustrious description which is in the contrast with the brutal dying of the elephants. This description comes from Orwell's story "Shooting an Elephant" in which his aim was to expose the evils of colonialism and show that all the people that are part of the imperialist powers are morally compromised.