Catherine, any tile guy worth anything, knows to take pebbles off the mesh to hand place them. I've done these pebble floors many times and even I know. I also know to stagger the sheets so you don't see 'grid lines'. and it's imperative that the tops of the pebbles have a sealer applied before install/grouting! what you see is all of the grout residue adhering to the pebbles. It's next to impossible to remove it if it's not sealed before grouting. (pebbles, like stone, have natural pits and cracks. grout gets imbedded in them if they aren't sealed).
he did a poor job. Way too much grout in between the rocks. plus, you have divots. Divots hold water. water will discolor the grout. He needs to know how to properly grout so he doesn't remove too much grout between the pebbles and make divots. When doing these against the walls, the pebbles need to be taken off the mesh so they can sit as close as possible to the tile. All that grout in between the pebble and vertical wall tiles should not be like that. look at my photo below and how nice the pebbles are against the walls. this can only be achieved by removing then from the mesh and placing them by hand. A lot more work that your lazy tile guy didn't want to do. The guy has no pride in his work.
your tile guy is a moron and making excuses for his poor work. call him out on his BS and have him rectify the issue of him ruining your tile. If he doesn't know how to lay these properly, he should have, A. done his homework, or B. hire someone who is familiar w/these.
He's responsible for the poor work, not you. don't pay him for this BS.
I laid these myself. one by one. I sealed the tops of the sheets prior,,,one by one. I grouted them myself. A lot of work? you bet. looks good tho doesn't it? (yes it's dated because it was done 7 years ago, but that's beside the point!) This was a house we flipped to sell, but are currently renting.
Q