Having been heavily linked with a move to Camp Nou for some time, the 27-year-old finally revealed the decision he had made on his future on the eve of World Cup duty.
In a lavish video documentary which aired his Barca snub, Griezmann claimed there are “things to do with Atletico”.
It appeared from the outside as though it had taken him some months to reach that conclusion, but Hernandez believes his fellow countryman was always staying in the Spanish capital.
He told reporters: “I believe Griezmann made his choice a month ago. The video only came recently but that [situation] wasn't in his head.
“He's only thinking about the World Cup and is 100 per cent focused on that.”
Griezmann also stated that he wished to avoid being “one more” at Barcelona, with Hernandez agreeing that joining a star-studded squad in Catalunya would have been the wrong choice.
He added: “I think like his wife said in an interview: ‘At Atletico, you can be a star. At Barcelona, you will only be a player’. She said what is most essential, that’s the truth.
“Here, at Atletico, he can be the idol of everyone, of every fan.
“If he would have gone to Barcelona, there are a lot of great players and the best player in the world as well. He would have been in the shadow of some great players like Messi, Iniesta or even Xavi before.
“If he would have moved to Barcelona, it would have only been one more player in the team.
“Here, at Atletico, he is the player, our best player, our leader. He will make the difference.”
Griezmann is already up and running as a talismanic presence for France at World Cup 2018, with a controversial penalty converted in a 2-1 victory over Australia in their opening fixture.
He was replaced by Olivier Giroud in that contest, having struggled to produce a spark outside of his spot kick, but has been assured by coach Didier Deschamps that his starting spot is not under threat.