The veteran centre-back brought an end to his trophy-laden 12-year stay at Old Trafford when his contract expired last season.
Subsequently, Ferdinand was reunited with QPR manager Harry Redknapp, who he worked under at his first club West Ham.
The 35-year-old is thrilled to be staying in the Premier League, but admitted that the deal may not have happened if Giggs had been named permanent manager at United instead of Louis van Gaal.
"Giggsy is one of my mates, I played with him for years," Ferdinand said. "We had that chat when he got the job, he had to look at it as if he would still be there and he did tell me I would have stayed and been a part of his plans.
"But things change quickly, the new manager came in and wanted a new direction. I dusted myself down and moved on.
"I said at the time that Man United would have to tell me they didn't want me for me to leave the club. That's what happened they said 'thank you and goodbye'.
"It has to be that way. The club is bigger than any player. I'm here now and I'm glad that Harry and [QPR chairman] Tony Fernandes gave me the chance to come here."
Ferdinand also confirmed he had other offers but the lure of moving back to London helped twist his arm.
He added: "I play to win whether that's a match or in training. We have to put points on the board. That's what we did at Man United that's what we'll do here. A successful season is staying in the Premier League.
"There were teams in the Premier League and teams abroad but when Harry gave me the call and the chance to return to London [I could not turn it down]."
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