Are cops taught to ume everyone is a liar?

I got pulled over for going 30 in a 25mph zone. I was polite, non defensive when the officer asked me if I had ever been pulled over before. I told him "no sir", and he got defensive and questioned me again. I repeated "no sir". He said in a condescending tone "we'll see if you are telling me the truth." He and a second officer looked into the windows of my SUV with a flashlight and spotted 7 soccer in a ball bag. He questioned what those were for and what was I doing with them. I said, Umm, I coach kindergarten soccer! I was getting fearful they were going to drag me out of the car and shove my face into the cement like you see on the show "COPS"...... They both then arrogantly stomped back to the flashing car. They were back there for 20min-30 minutes. The first officer came back and let me know I had a perfect driving record and let me off with a warning. He even said "have a nice day mam".... Now, why would he ume I was lying to him in the first place? Do they teach officers in training to be an *** at first to everyone they pull over?