Data was promoted to First Officer of the Enterrprise-E, his promotion of Commander likely was n the pipeline (though not necessary for First Officer, arguably.) "Commander" was often, if not always, used as shorthand for the Lt. Commander rank in all of Trek.
The interviewer may have either mis-spoken or was being intentionally condescending/dismissive of Data's rank since he was a "synth" to rile Picard or because that's just who she is, that or she didn't know about a posthumous promotion Data was given because of his sacrifice for Picard and The Federation or it was in the pipeline already pending him officially taking the FO position on the ship, hence the Data file's presentation of the rank. That or a flat out inconsistency, the line from the reporter was for "our" sake so we we wouldn't go "Uh-uh! Data was a Lieutenant Commander!" and we weren't supposed to notice the file thing.
One way or another, nothing to see here. The only thing worth noting is the discrepancy in what he's called and what the file said.
But Lt. Commanders were always called "Commander" for short unless it was some formal thing where the entire rank was used for respect. Geordi, Crusher, Troi, Data, Chakotay whoever else throughout the entirety of the franchise who held the rank of Lt. Commander was called simply "Commander" for short.
Just like in the first season Geordi is called simply "Lieutenant La Forge" and not "Lieutenant, Junior Grade La Forge."
