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.