Synthetic Blend Oil? Gimmick?

Great information....
Given that I'm not a petroleum engineer or good at reading ASTM standards would it be fair to say that technically a synthetic blend can be made of 100% conventional oil and be called "synthetic blend" as long as "PERFORMS" like a synthetic blend, even thought there is nothing synthetic in the blend?
How this makes sense.. just trying to understand what is synthetic in the blend.
Appreciate the comments.