It's ironic because it provides a subversion of expectations: the FTC is releasing a statement in which they are trying to demonstrate some sort of power and authority over Facebook, but at the same time using one of Facebook's product, thereby undermining (in a very minor way) their own statement. It's not deeply ironic, but it's definitely an example of irony.

Source: My partner wrote his doctoral dissertation on irony, so I happen to have picked up an appreciation for the subject.