Manchester United released the striker last month after he spent last season on loan at Pittodrie.
The 22-year-old joined United's academy as a seven-year-old.
Wilson said: "There is a lot of money in football these days and sometimes that can be the deciding factor.
"But for me, at this point, the big thing was about being content, comfortable and happy and I am just ready to work for the team I have been integrated to and I look forward to that.
"The group of players is brilliant. I really enjoyed working with the staff and everyone behind the scenes. I haven't got a bad word to say, that is why I'm back here.
"There were other offers but this was a fairly easy decision for me to make."
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