J.J. Spaun sat quietly Tuesday morning at Shinnecock Hills while USGA officials conducted a media day presentation for next month’s U.S. Open at the venerable Long Island 18-hole icon. “I still can’t believe I won this tournament , honestly,’’ Spaun said, sounding like the most humble major champion ever. The 35-year-old Spaun, a late bloomer, will defend his title when the first round begins at Shinnecock on June 18. He called his existence the past 11 months as the reigning U.S. Open champion, in only his second start in the major, “very strange.’’ “I remember getting to the Travelers Championship [the week after the U.S. Open] and I was paired with Scottie [Scheffler, the world No. 1] and all of a sudden there were like 10,000 people around the first tee,’’ Spaun said. “I got to go first, which was nice. They announced me as the U.S. Open champion and it was almost like I had to step off and really let that sink in … just to hear the crowd go crazy.…