Can they charge me for controlled substance after they let me go with simply issueing a citation for drug paraphanerlia?

I received a citation for drug paraphernalia in Dallas, Texas. At the time of the incident when asked if I could be searched I replied no upon which the police officer requested a K9 unit. In the meantime the officer was very unprofessional and was giving threats such as I will fuck up your life if I find anything. Upon the search they found hash which is a controlled substance. The officer asked me what it was but I was not responding. He then gave me a choice of telling him and not going to jail and simply getting a ticket. I ended up telling him and he gave me a citation. Weeks later I get pulled over and find out I have warrant on my name for controlled substance from the same incident. I don't understand how could he give me a ticket and then weeks later charge me and issue a warrant for the same offense he let me off from.