I believe this rule was discussed, but it evidently wasn’t implemented as it isn’t in the Sporting Regulations. As long as Ferrari were using “demonstration” tyres provided specifically for the occasion, the demo run was legal.
The use of those tyres, incidentally, would probably have rendered any data gathered from the tests essentially worthless for competitive use.
Even so, I find it incredible that an F1 website would publish such an article without first bothering to check the relevant regulations. It’s not as if they’re hard to get hold of, being freely available on the FIA website.
I’m not in favour of the testing ban, so I’m not particularly concerned if they are purposely pushing the rules.
I think the test more served as an installation of new parts than a proper test. If you bring new parts to a GP that have already been run on the car in testing, you are at an advantage over teams that will have to use up time in FP1 getting everything working.
But there was a rule introduced in 2010 that said if a team wants to hold a filming day, the car must be of the same speciication as that used at the previous race. It was introduced when Ferrari had a filming day ahead of the European Grand Prix when they were introducing a major update (I think it was a blown diffuser) that was run on the filming day. A lot of people though Ferrari were trying to slip beneath the radar because of the complexity of the system and the potential to get it wrong.