It's just a simple flat render over a blockwork construction (cement bricks).

This is a beautiful pebble mosaic walkway. Is the black design in the middle is also pebbles. How many people and how long did it take to create?

Yes the black section is also a pebble. It was just me, one man. From memory I think it took a little over two days in total. Two to lay and half mucking about with grout and sealer. I used an enhancing sealer to ensure the contrasts of the stones and grout. For feature work like this I always recommend using a grout additive for added stability, flexibility and stain resistance. The mortar compound I laid in also had an additive 'Bondcrete' in it and was tinted to grout colour :)