What does Hebrews 13:23 mean?

Scholars differ in their opinion of who wrote the book of Hebrews. The author most commonly attributed to this letter is the apostle Paul, and references such as this are among the reasons why. Timothy was a student and friend of Paul (1 Timothy 1:1–2) who travelled with him on his missionary journeys. Eventually, Timothy was left in charge of a series of churches, during one of Paul's terms in prison. At the end of his life, sensing his impending execution, Paul wrote his last words recorded in the New Testament, the letter of 2 Timothy.

This verse speaks of Timothy's "release," which is almost always interpreted to mean being let go from a Roman prison. This would make sense, given the history of Paul and his travelling companions. At the same time, the Greek of this passage might mean that Timothy has been "sent out," possibly implying that he is the one carrying this letter to the readers.