Yes I am guilty of moral relativism, that I am not alone in that is interesting, so the article is one I find interesting. But it is flawed, your example is apt and that's not the only one:

Me: “I believe that George Washington was the first president. Is that a fact or an opinion?”

Him: “It’s a fact.”

Me: “But I believe it, and you said that what someone believes is an opinion.”

Him: “Yeah, but it’s true.”

Me: “So it’s both a fact and an opinion?”

The blank stare on his face said it all.

...

I also tend to stare blankly at people when I'm thinking "Duh" too. He could have done better than accept a blank stare as freedom to interpret whatever he wanted.

With a mathematical operator: Fact > Opinion, one is a higher form of truth.