What is the deal with Yoel Romero?

I watched a video where both Luke Rockhold and Whittaker were talking about him and they said that he felt like he was made out of steel. They both said that punching and kicking him actually hurt their hands and feet since it was like kicking concrete. Not to mention that Yoel seemed unfazed by any kind of strike, whether it was a headkick or livershot. I’ve never heard this kind of description about any other fighter.

Another story where after he got his orbital bone fractured by Whittaker, the doctor who examined him said that his tendons were 4x larger than a normal human’s and that his orbital bone was already healing by itself. Apparently the doctor had never seen a human being like him.

Was he a part of some Cuban government super soldier experiment or something? Obviously he was on PEDs but how come he seems to be an anomaly? Surely, everyone in the UFC is on the same shit he was on but I’ve never heard anyone talk about a fighter they way they describe Romero.