Link worked. Maybe you fixed it soon enough to not show here was an edit.

This looks like IKEA shelving, but even if those back panels are actual wood, they're probably 1/4" thick and might be spaced as much as a half inch off the wall. Don't even think about mounting anything there until you have taken apart the unit that the TV will mount to so you can see exactly what the dimensioning is on the back.

Don't hit one stud. Hit two. If you can't hit more than one, then install togglers (not, and NEVER, toggle bolts) and spacers at the top and bottom left and right of the mount, and tell the client to be gentle with the TV.

So, if the back panels are spaced off the wall, drill holes where the studs are (you have to remove the back panel to find the studs) and add spacers between the drywall or whatever is back there so that there is no open space, front to back, between the front of the mounting bolt and the wood that you sink it into. If you have to install togglers, put similar spacers between the front of the bolt and the drywall.

Actually....
If the back panel is off the wall, why not remove as much drywall as you have to in order to get EXACTLY into the studs? That section will be behind the shelving's back panel, so the lack of drywall won't show.

EDIT: Oh, yeah: you said "this TV." Is that TV a 55? Do you have to demo any of the unit to get it to fit widthwise?