The Brazilian completed a world-record move to Paris Saint-Germain on August 3, 11 days after Pique posted a photo of the pair and the caption "se queda".
Speaking at a press conference ahead of Barca's Supercopa de Espana meeting with Real Madrid, he said: "At [Lionel] Messi's wedding [at the end of June], I had an idea that he might leave.
"In pre-season, again, he said he would leave. When I wrote the 'he's staying' tweet, I knew 100% that he was leaving.
"I know that he has his reasons, they could be financial, or it could be to be the best player in the world. He shouldn't be judged, he's a brave player. He performed extraordinarily for us.
"He hasn't disappointed me, and I don't regret the 'he's staying' tweet. Everything has a reason, and I wanted to use social media because that's an instrument I have. I wanted to help the club, and at least I tried, even though I knew he had made his decision."
During his four years at Camp Nou, Neymar won two La Liga titles, the Champions League and three Copas del Rey.