If it makes you feel any better Stan, getting "an average time" is far better than a time equal to "an average player's average time". I wouldn't be surprised at all that you are faster than half the users here, just because there are so many users who solve 1-3 puzzles, and then quit, and never try another puzzle.
I wouldn't be surprised if half the puzzles solved are solved by the same 5% of users. The people trying to get trophies are solving thousands of puzzles each month, and so seeing how your time compares to the others in the graph is basically showing how you compare with that small group of people. For each person in the top 50, there are probably hundreds who get frustrated and quit after doing just a few puzzles.