The Array plot block is used to plot vectors or arrays.
The X-axis shown in the array plot block is samples of different vectors at the same time-step. (The X-tick may or may not be integers though, depends on sample increment)
The x-axis is not the time step of your simulation nor the sample time of the input (signal) block.
If the input to Array plot block is a vector v = [1,2,3,4], and if you set the sample increment to 1, after the simulation
x-axis = 0 ,1 ,2, 3
y-axis = 1 ,2 ,3 ,4
will be the output of the Array Plot block.
That is, at a given time step, input to the Array plot block is (a scalar or) a 1-element vector. So the array plot block, plots the entire sine wave at x=0 (which corresponds to vector 1), which you see at the end of your simulation.
To Visualize a discrete or a continuous sine wave, refer to the scope
Kiran Felix Robert