That’s just a random picture, not my house, but what happens is lutron makes a piece that fits into the wall Where the switchbox is and holds the pico in place even though it’s not wired in. So you remove an existing wall switch and put the pico there. So what actually is going into the wall, not just surface mount.
https://www.amazon.com/Caseta-Wireless-Wallplate-Bracket-PICO-WBX-ADAPT/dp/B00JZRAFEA
If you want to surfacemount it and have it look like a double gang switch you need to get a switch box extension piece that lifts the wired switch up a little bit to match the pico position.
The extension pieces are cheap, usually two or three dollars, and you can get them at a Home Depot. People use them when they have tiled around an existing switch area In a bathroom or kitchen. So that gives you an extra 3/4 of an inch or so.
There’s a topic in the forums discussing those for people who bought a smart switch which is too thick for their existing switchbox, it might give you some ideas:
sorry, I just realized you were not the original poster for this thread, and we are getting very far off topic. Please start your own thread on wall mounting Lutron Picos and we can talk there. 