I am not a lawyer, but I am inclined to agree with you. However, the analysis for whether an employee's actions trigger
respondeat superior is more complicated than that, especially for employees where the work/life balance may not be entirely clear (this is frequently true of executives and may be true of anyone that ever does post/publish/or even speak on behalf of the company).
But even if it were clear that the employee's actions did not fall into the category, a company is rightly concerned about anything that would create even a colorable cause of action (in otherwords, anything someone could sue for without it being immediately thrown out).
Also, the company might be worried about the appearance in the public's eyes even when lawsuits are entirely off the table.