I believe I do have a timeline of events that you might find illuminating.
The man tells him they have never met, but that he had always wanted to meet him. He then recites this short poem:
I had a walrus for a pet.
Why I bought it, I forget.
I fed it kedgeree and rusks,
And used best Blanco on his tusks.
From the style of the rhyme, Newt recognises it as something written by himself or Jerry. He remarks that animals and kings were their speciality.
Newt is gratified to hear that the man had remembered the verse for all these years and that it had “worked”.