Tiger's in this alone. Tiger has just completed the most remarkable 12 months of golf in professional history. He won the U.S. Open, British Open, the PGA and the Masters in succession. Let's not get into a debate. Tiger didn't win the Grand Slam, because he didn't win all four majors in the same calendar year.
Tiger is a golf historian.
He knows it's not the Grand Slam. Over the last 40 or so years there have been few bursts that compare to it. Of course, in tennis you play whomever advances through the draw. In golf, you must beat everyone in the field. Michael Johnson was untouchable in 1995 and 1996.