Goodman also cited a general manager who called him the "most underrated guy in the draft."
The power forward was the Big Ten Player of the Year and a consensus All-American after averaging 18.5 points and 12.5 rebounds per game last season.
Swanigan hadn't signed an agent and was able to return to school until Wednesday's deadline.
He posted thank-you messages to Purdue fans on his Twitter and Instagram accounts:
Mamba Forever @calebswanigan50
Never thought I'd be sad to say that I am going to chase my reality in the NBA. Y'all got my love forever. #boilerup2017-5-24 21:32:28
Despite his impressive statistics from this past season, the 6'9", 245-pound forward is considered a bit undersized for the NBA without elite athleticism. This keeps him ranked just No. 35 overall in the 2017 class by DraftExpress.
Still, it would be difficult for Swanigan to have a better year than he had in 2016-17, making his decision to stay in the draft a wise one.