He didn't even say it was Gerry himself who reminded him of the man he saw - it was the way he was holding/carrying his sleeping child that looked familiar to him. His memory had not been jogged by all the pictures of Gerry that he must have seen previously on TV and in the Press.
Right. It wasn't his face (nobody said so), but the uncomfortable holding that... struck him, which is coherent with his assumed incapacity to recognize the carrier. You don't expect a father to hold his child clumsily and this detail is likely kept in memory.
I never understood what was clumsy in the way Gerry carried Sean down the steps of an aircraft.
The little boy was, and stayed, sound asleep (despite getting out of seats, out of the plane, all the noise on a tarmac).
This little boy was totally limp in his daddy's arms and his daddy was obviously looking down to see where he was going.
There aren't 10,000 ways to carry a child of that age down such steps.
Could THAT similarity have triggered a flash memory?