In things fall apart, why is it ironic that okonkwos gun leads to his extile in chapter 13?

Okonkwos' gun went off during the burial of Ogbuefi Ezeudu who warned him against taking part in the death of Ikemefuna. The process killed Ezeudu's son who was only sixteen year-old. This is quite ironic because initially Ezeudu warned Okonkwos against committing a sin which he still was not able to escape from due to the accident.