Wrong.
They asked if using it to maintain stability under braking was legal. The FIA said yes, as it broke no rules.
Then when the full details were revealed it actually transpired that they were using a mechanical moving device to maintain an aero benefit primarily, which was then deemed illegal under the rules banning movable aero parts.
The FIA didn't ignore some rules and then decide to impose them, the actual purpose of the device changed as it was developed and details revealed.
Its all to do with what something's 'primary' purpose is. For example, the suspension struts all move, and they are all aerodynamically shaped to offer the least drag and also in the case of some of the rear parts, channel air to improve aerodynamics. The FIA haven't banned anything but round suspension parts because at the end of the day a suspensions primary purpose is to hold the wheels on and the car up.
When Lotus were initially developing the device they convinced the FIA its primary purpose was to stabalise the car under braking by altering the weight transfer. As the device developed however the FIA came to the conclusion that its primary purpose was instead to maintain ride height for an aero advantage, and therefore rightly banned it. Rather similar to the iconic 'fan car' where they managed to convince the FIA its primary purpose was cooling, before the FIA took a closer look and called shenanigans.
So no, the FIA didn't blindly ignore a bunch of rules. And seen as the device never made it onto a track for a competitive weekend anyway, its irrelevant. It was never used in a situation where it would have been subject to the rules.