That's the first sanction...
You'd be free to, but you'd be wrong. Reports are not automatically followed through with sanctions. They are manually investigated, and if found to be without merit the person who submitted the report is sanctioned. For you to get a warning, you have done something wrong.
Whether you believe it or not, for you to get a warning from PSN that you have breached the TOS, you have breached the TOS.
Look more carefully at what you were doing on the day the message refers to.