Apply Dimensions to the array to see its structure.
First example at ref/ListVectorPlot3D
In[73]:= Dimensions[
Table[{x, y, z}, {x, -1, 1, .1}, {y, -1, 1, .1}, {z, -1, 1, .1}]]
Out[73]= {21, 21, 21, 3}
Second example there:
In[74]:= Dimensions[
Table[{{x, y, z}, {y, x - x^3, z}}, {x, -1.5, 1.5, 0.2}, {y, -2, 2,
0.2}, {z, -1, 1, 0.1}]]
Out[74]= {16, 21, 21, 2, 3}