Three related concepts must be separated. Contemporaneity means that two narrators were alive in the same period. Possibility of meeting requires compatible ages and circumstances. Proof of hearing is evidence that a specific act of transmission occurred.
Two men who lived in Egypt and Khurāsān respectively might be contemporaries without having met. Evidence that one travelled to the other’s city improves the possibility, but a clear audition statement or other credible evidence may still be necessary.
Rule: Do not elevate chronological possibility into proof of actual hearing without sufficient grounds.