Engineered Fluids' Dielectric Coolants are hydrocarbon based. This means that the molecular structure is made of hydrogen and carbon. They're non-toxic and biodegradable - and have even been classified as "Food Grade" by the U.S. Department of Agriculture.
Fluorinated solvents such as FC-770 are based on a completely different chemistry. They're toxic, not biodegradable, and not compatible with hydrocarbon-based products.