The energy density is somewhere around 26 MJ/L for LNG vs 36MJ/L for diesel...what do you bet the conversion in the chart above is by volume? If you convert by energy density, diesel and LNG look to be priced exactly the same (or pretty close).
Also, what is keeping this company from just buying a tanker full of fuel and refueling at their warehouse?
I suspect that there are dozens of zoning, fire, and other safety regs that would apply. In leased facilities, there are probably also lease restrictions.
If you look at the second chart Thackney posted, the price per megajoule is listed, and CNG comes in about $11/MJ cheaper.
Gasoline: $29.85/MJ
CNG: $18.07/MJ