Same thing happened to me few years ago. in 3C on a flight to MSP, get up as row 2 is walking out, the bin is open but my carry-on is gone.
Looked into bins on other side and the adjacent ones thinking someone moved it but no luck... at this time I am holding up everyone and start to get dirty looks so just take the laptop bag and come out. And I see a guy in the jet bridge holding my bag.
I thanked him for help! he was suitably embarrassed and went swimming upstream to retrieve his bag.
Lesson learned. Bought a pair bright yellow shoelaces and wrapped tightly on both handles of my carry-on. no one has ever mistaken this for their bag since.