Although Wolves signed 10 players in deals worth £67m this summer following promotion to the Premier League, some fans were angered when the 28-year-old was moved on from Molineux.
Douglas was an ever-present figure in helping the West Midlanders to the Championship title and back into the top flight with 14 assists last term.
"I can see why people would question it on the face of it," Thelwell told the Express & Star. "Barry is a top professional, a top person and had an exceptional and outstanding season – he should be very proud of what he did for Wolves.
"Things change for a lot of different reasons – that's football. You get to the point where we have to do the best thing for Wolves. Players come in with different characteristics and it should be remembered that Barry had one year left on his contract.
"Hopefully we found a solution where everyone feels they've been able to move forward. Barry is now at the top of the Championship in a very big team and we wish him all the best – him and his family were nothing but a pleasure to deal with."
Douglas returned to the United Kingdom with Wolves in 2017 following a year at Konyaspor and three seasons with Lech Poznan.