What was ironic about Johnny’s note to Mr. John Hancock and the sugar basin he noticed in his home?

Johnny notices that Mr. Hancock did find a silversmith to make and match a sugar basin to his set after Mr. Lapham failed so miserably to meet his request. He realizes the silversmith made the same mistake he did and later corrected after talking with Paul Revere. The irony is that Johnny knew that mistake would be made but when he delivered the note, he was ironicly correct.