"I'd be surprised if I received an email like that from a student, because I think normally there is a level of distance between a student and a principal," she said.
But the male principal told the tribunal that he was a mentor to many of his students in his eight years at the school.
He has now moved to another school, but is charged with using Facebook to interact with current and/or past students after resigning from the first school, despite being asked not to by its board of trustees.
While he was at the school, he was directly in charge of its "leadership academy" and is charged with "disproportionate spending of school funds for leadership academy activities".
A forensic accountant gave evidence that spending on the academy in 2014 exceeded the income allocated to it by more than $40,000.
The dinner with the former female student was alleged to have taken place in another city. The principal is alleged to have arranged to return from a school visit to Singapore via that city at school expense.
The accountant said the principal paid $118.50 on his school credit card for the dinner, described on the receipt as "food and alcoholic beverages".
She said it was "quite common" for former leadership academy students to return to the school and have lunch in the cafe, with the costs coded to the principal's expenses.
Lawyer Claire Patterson, representing the Teaching Council's complaints investigation committee, cited one email in which a former student, who was then at high school, told the principal that she wanted to visit to "catch up".
"What would be a good day to wag school and come in?" the student asked.
The principal replied: "Love to have you pop in. Wednesday afternoon is good or Thursday any time from 12.30pm. Not meant to wag school ... but kids do."
In other emails, he agreed to pay $250 to one former student and $150 to another to support the ex-students' fundraising efforts.
Patterson said the principal did not tell off the students who told him they "missed" and "loved" him, but "let such emails slide by without a rebuke".
She said the late-night Facebook chat was in a private group with 16 members, including students, after the principal had moved to another town.
"Here's hoping you can all come up to [his new town]," he told the group in one post.
"Sad to hear your news," he told another female student.
"Nighty night, sir," one of the students replied, with a heart emoji.
However the principal told the tribunal that the chat exposed his "inadequacy" with social media.
"I actually didn't realise initially that I was in a group chat," he said.
He said his approach was different from the other principal who gave evidence.
"My style is different. I would stand at the school gate every day before and after school welcoming the children," he said.
"I ran our rugby team, I ran the school council, I ran the leadership academy. I was a mentor to those children."
He said former students were often brought back to help with arts, dance, kapa haka and sports teams.
"Where possible, we were trying to show our appreciation with koha or kai," he said.
He said the girl whom he took out to dinner came back while she was at high school to coach netball and kapa haka for two years and then helped with the leadership academy for another year.
"We gave her a koha at the end of 2013 when she went to university," he said.
"She went to university and a year or two later we put her on the payroll and gave her one or two payments a year."
He said the girl was a role model for younger students.
"Not a lot of our kids came from families that went to university, so what she provided was a real-life confirmation: 'I was you, you can do this, stick through to Year 13, go to [university],'" he said.
The principal said he could not recall the alleged interview with a student behind closed doors at 7.30am, but he said he made a practice of one-to-one "conferences" with every child in the school for 10 to 15 minutes each twice a year.
"I just had a talk to them about their involvement in the school - any concerns, any suggestions, because I wanted to know every child at the school," he said.
He said many of the children invited to join the leadership academy were "at-risk" students.
"To be frank, the goal was to make sure these children didn't end up with a [gang] patch on their back," he said.
"I wanted to engage with them. The constant focus was to increase their attendance rate and good behaviour. A lot of these initiatives were about enticing the children to be part of a positive learning environment."
The tribunal hearing is continuing.
