"My actions constituted pure hacking that resulted in relatively trivial expenses for the companies involved, despite the government's false claims"

This quote by Kevin Mitnick is referring to his own actions as a hacker. He is declaring that his actions were simply hacking, which the federal government's claims of the expenditures sustained by the business included were false. He is indicating that the expenses were reasonably insignificant, and that the federal government was overemphasizing the costs. This could be translated as Mitnick trying to minimize the seriousness of his actions, or it could be viewed as him trying to mention the federal government's exaggeration of the costs. In any case, it is clear that Mitnick is attempting to safeguard his actions and the costs related to them.