Ha, very true. Yay double standards.
Is it really though? The clear differential is that Suzie Wolf is actually an employee of the FIA and leaking confidential FIA information to a third party is gross misconduct. Any suspicion of gross misconduct should be internally investigated as it would be at any employer.
The FIA can't sack Horner because they don't employ him. At best they can kick RB out of F1 for bringing it into disrepute which is a hard argument based on the currently available information.
Edit: to be clear an investigation should be just that, an investigation. If nothing was found to be untoward, happy days and move on. If something untoward is found, appropriate action is taken.