Perhaps the OP is surprised that the mean - 1 S.D. is a negative number (especially where the minimum is 0).
Here are two examples that may clarify.
Suppose you have a class of 20 first graders, where 18 are 6 years old, 1 is 5, and 1 is 7. Now add in the 49-year-old teacher. The average age is 8.0, while the standard deviation is 9.402.
You might be thinking: one standard deviation ranges for this class ranges from -1.402 to 17.402 years. You might be surprised that the S.D. includes a negative age, which seems unreasonable.
You don't have to worry about the negative age (or the 3D plots extending less than the minimum of 0.0). Intuitively, you still have about two-thirds of the data within 1 S.D. of the mean. (You actually have 95% of the data within 2 S.D. of the mean.)
When the data takes on a non-normal distribution, you will see surprising results like this.
Second example. In his book, Fooled by Randomness, Nassim Taleb sets up the thought experiment of a blindfolded archer shooting at a wall of inifinte length. The archer can shoot between +90 degrees and -90 degrees.
Every once in a while, the archer will shoot the arrow parallel to the wall, and it will never hit. Consider how far the arrow misses the target as the distribution of numbers. The standard deviation for this scenario would be inifinte.