The above reply hit the nail on the head. The FDA allows these little loopholes that allow food manufacturers to legally lie.
Those cans are 100% pure fat.
By law anything that has less than .5g of fat per serving can be labeled fat free.
1/3 of a second is around .26 g IIRC, and as any 6th grade math wiz can tell you, there's less than 1/2 of anything in a 1/4.