On 9/8/94 a US Air 737 in Pittsburgh just fell out of the air on final approach killing all on board. The crash was blamed on an uncommanded rudder movement, and all 737's had to be modified to (partially) avoid the problem.
Airbus doesn't have a monopoly on design flaws.
Obviously you ground a fleet to fix a mechanical problem that kills people.
They didn't ground any airplanes after that Airbus' tail just sorta fell off.
We were even especially mad at france that week. What better time to stick it to them? What better excuse?
No groundings, therefore no mechanical failure, therefore the government knew it was terrorism.