It's not a slam but it's the next best thing in tennis and every sportsman in the world wants to win an Olympic gold medal. He beat Djoko and demolished Fed, it's an outstanding achievement.
Tennis tier of importance:
1) Slams
-Wimbledon
-U.S. Open
-French Open
-Australian Open
2) World Tour Finals
3) Olympics
4) Masters
So technically, a gold medal is the 6th most important title in tennis.