I didn't take out my water bottle from my bag once, because I wasn't aware I was going to have to go through security a second time when arriving in the US from

I didn't take out my water bottle from my bag once, because I wasn't aware I was going to have to go through security a second time when arriving in the US from an international flight. It had one sip of water in it. I told them I would just drink the sip of water, unacceptable. The TSA employee told me that if I dumped it or drank it, that was fine, but I'd have to get in back of the line again. Why? I don't know. He sat there holding my water bottle saying "I'll only give it to you if you'll get in back of the line." I finally said fine, keep it. I still don't understand why I could drink it and get in back of the line, but I couldn't drink it and stay in front of the line. It seemed to me like he was just power tripping.