He was the one saying "I found such and such.."

So the same question you pose could even be said of someone even going so far as to just say "I found a treasure" . Whether or not they posted a picture. Ie.: wouldn't they be afraid of even saying only that?
But to answer your question, people post pictures in the show and tell on the Forum all the time. Yes, even valuable goodies get shown on the Forum.
Not that someone couldn't have the logic you speak of. But at a certain point, the line of reasoning that you speak of, could be set to bolster any claim. And make it un-assailable, etc....