The Health and Disability Commission said staff failed to do enough to investigate the extent of the disease and whether the man had developed complications.
Te Kōhao Health tumuaki Lady Tureiti Moxon told Morning Report this was not an unusual case.
"This happens very often, and more often than not it is because people have a particular kind of view of who they're dealing with instead of our professionals thinking of them as people and doing the best by the people that are before them."
She said one of the issues with Māori health in the country was that people were dying prematurely from preventable diseases because they were not being given the diagnostic tests they needed.
"They should have looked at him and said 'OK, five times, that's a record surely', but no 'will send them home ... go to bed, take aspirin, take a Panadol and then you'll be all right in the morning'. And then they don't wake up."
She said people needed to be put at the centre of health care in New Zealand.
Moxon hoped the Māori Health Authority would focus on prevention rather than cure.
Hospitals come under Te Whatu Ora - NZ Health Authority.
Te Whānau Haunui chief executive Simon Royal said Māori had long had concerns about fair and equitable public health treatment.
He said negative views of hospitals are common and many Māori perceived them as a place to go to die.
Royal said clinician bias had gone on for too long and the monocultural health approach needed to end.
In a statement, Whanganui Hospital said it had made changes to try to avoid cultural barriers and miscommunications since the man's death.
New staff must do equity and cultural inclusion training, and it has a team to help Māori patients navigate the system, a spokesperson said.
The changes had been in place for two years but it was continuing to monitor its ED carefully, they said.
"Te Whatu Ora - Health New Zealand Whanganui expresses its deepest sympathies to all involved in this very sad situation, particularly the whānau who have been grieving the loss of their loved one."