That's why you got the ticket. As Jay said....the new owner never transferred the title.
Here in WA state on the bottom of each title there is a tear off that the seller is supposed to fill out and send in to the DMV. That protects the seller since once the state receives the seller's portion of the title the state enters that info into the records.
I always make sure I send in that portion just to protect myself. What if the new buyer doesn't transfer it and has a major accident and runs away. They never catch the guy or even know who's driving. Guess who's on the hook.