You can indeed find crystal affixes in legit eternals by luck or by Crafting with dust many times with Crystalline. RNG be on your side for that one but I've found plenty of them.
It's only not ok if the eternal is modified to have crystal affix.
E.g, Eternal Steigers Fortune but with 20% Weaken crystal affix as well as a set affix in the eternal and other things that make the eternal count as modified. The original Steigers Fortune sword has no set affix and is comprised of farm affixes .
I have a feeling some of the reported ones are fishy but there are others that are justified to be reported (e.g modified pet, eternal, crystal affix on pet, legend affix on pet, etc).