The winning numbers (4, 5, 6, 8, 11, 16) are derived from f-stops on a camera. As Freddie was a professional photographer, it is presumed he always played those numbers. Columbo noted that and Uncle Leon responded that he was a helluva photographer and knew those numbers like the back of his hand.
I believe that Leon said that he had just picked the lottery numbers at random. But when Columbo noticed that the numbers were taken from a camera, it became obvious to Columbo that Freddie was the real owner of the ticket. Columbo now saw the motive for Freddy’s murder.