I feel like this photo is successful as it uses really strong depth of field to show what is near and what is far. Although the DoF is artificial, it is pretty smooth and almost mimics how a macro lens would capture a photo like this. The photo is also successful through the use of leading lines with the sidewalk edge and diminishing scale with the other subject behind it.
So DoF refers to the focus. The shrub further away looks out of focus.
The difference in scale between the two which gives a sense of space (or depth) is perspective. The converging lines of the curb and the lines painted on the street are also perspective and create a sense of deep space on what is a flat 2D surface.