An on-screen guide describes the documentary and the channel also carries a warning that its content is not suitable for children.
Enright said crew were able to block content to the seat of unaccompanied minors at the request of parents.
Programmes were selected according to the quality of content, box office ratings, topicality, and customer demographics, he said.
On Air New Zealand flights a number of films carry an R rating, meaning passengers aged under-17 may only watch them with an accompanying parent or adult.
Cabin crew could lock out certain programmes for unaccompanied minors who sat close to crew, said spokesman Mark Street.
Victoria University director of sociology Kevin Dew said showing the orgasm documentary as Qantas in-flight entertainment was "extending it a bit far".
"It does make you worry and think, 'will they then put some soft porn on?' It seems unsavoury to me," he said.
Dew said long-haul flights brought together people with different values in a small space, and passengers could not choose whom they sat next to.
Offering this film as part of the in-flight entertainment then strayed into "difficult territory".
"It strikes me as somewhat bizarre," he said. "I would think airlines would err on the side of conservative."
