I'm no chemist, but I can tell you that in the U.S. a "fatfree" product is
supposed to be truly fatfree (maybe a trace of fat is allowed in, that's
where I'd need the chemist to be sure). Most dairy products where I live are
available in a regular, reduced fat, or fatfree version - i.e. regular sour
cream, reduced fat free sour cream (maybe 1/2 the fat of regular - I'm not
sure the exact fat reduction, but I believe there are regulations defining
how much fat must be removed) and fat free sour cream.
Hope that's helpful.