What is this cops problem?

i got pulled over for not wearing my seatbelt yes i broke the law ok i admit it but i was driveing 65-70 on the interstate the cop was in the median shooting for speeders since i wasnt speeding he couldnt get me on that but i saw him pull out when i was about 1/4 mile down the road i realized i didnt have my seat belt on so i put it on. The cop comes raceing up beside me and is stareing at me at that time i had my seat belt on and was doing 55 in a 55mph construction zone then he gets behind me and turns his lights on he goes and looks under my car and all in my back seat i ask him if i was speeding and he says no seatbelt which i still have on and i say ya he responds you didnt have it on back there. he asked me why i explained i forgot after haveing a fight with my gf and i had just gotten on the interstate. he still wrote me a ticket 55$ i say thats bs i guess my gf aint getting an appology letter and a dozen roses lol what do you think i know i broke the law but was he a prick?