You say this in a very certain tone, but I am aware that the precise meaning of the word pais in this passage is hotly debated, ranging from "beloved servant" to "adopted son," and even "homosexual partner". Indeed, Strong's records a wide range of possible definitions, and there are hardly enough contextual cues to make a sure determination. Most translations describe the boy as a servant, which seems like a safe conclusion.In this case the servant is what we'd call in today's army an "Aide". It's a very respectable position especially for officers.
Regardless, whether the boy is a servant, aide or male lover to the centurion, what stands is that Jesus (and, later, his apostles) healed many sinners, without enumerating every sin they were guilty of before or after. For this reason, the argument that "he didn't say anything given the opportunity" (i.e. argument from silence) seems a little weak to me.