The Ombudsman made clear that every case depended on the context.
Professor Cheer said the OIA did contain similar protections to the Evidence Act provisions for journalists to protect their sources.
It allowed information to be withheld which was genuinely confidential, where a promise of confidentiality had been given, or where releasing the information could prejudice the supply of similar information or cause the source to dry up.
"So, yes, journalists should be careful about the off-the-cuff texts they send to ministers, and if they are worried at all, should make sure the text is the subject of an undertaking of confidentiality or at least labelled confidential."
Professor Cheer said even that might not be enough if there was enough public interest in it. "Even confidential texts may be released in the public interest unless there is a risk of a chilling effect or there is a greater public interest in withholding."
She said that in Glucina's case, there was little privacy interest because the gossip columnist had intended to publish the interview she was texting about. Nor was there any indication of a promise of confidentiality, Professor Cheer said.
"Rachel Glucina put the matter she refers to in the text into the public eye herself. She clearly did not regard it as confidential and there is no suggestion Key promised to keep it secret."
Professor Cheer said that in this case, there were also questions about whether Glucina was acting as a journalist, after the waitress said she was told Glucina was a public relations agent. The Press Council had upheld a complaint that she had not disclosed her role properly.
The professor said there was no reason a text could not be considered "official information", because the definition of that term was so broad.