In the version I know about Mrs Smith said and I paraphrase:
"I have nothing to add so p**s off Sooty".
Which is some distance from your version.
On which version I wonder will the sportsmen lay their purses?
There is nothing objective to establish context in the accessible files for the moment.
A possibility, however, is that Mr Smith, Sr., had a sudden recollection of how the child was carried, based on watching the news of Gerry coming down the plane with a sleeping Sean. A disturbing thought. He could have discussed the possibility with his wife and whether or not he should mention it to the police. Wife thinks, "Well, you never know, could be. Go ahead and ring. No harm done." Meanwhile, he's left with this dilemma: to ring or not to ring. He did.
Grandad did check with his children, who didn't think it was him and he also pointed that out.
In the same circumstances, I probably would have done as well - just on the off-chance that it could have been, based on a vague recollection. And then it's up to the police to work it out.
In theory.
I doubt that he expected that confidential doubt to end up splashed all over the media... and later exaggerated by the coordinator.