With his rhetorical question, he's saying it must be malice because no museum operator would be that incompetent. They're actively making a false claim to their customers. They could have just not said anything about the age of the toys since they know they didn't verify it. I think you can see this must be the case since you didn't answer his question.
In my country, if a business makes a factual claim about its products, it has to have already verified the correctness of it to some reasonable level and have the documentation so show that. There's no room for this "oh, I just assumed it was true because I'm incompetent" excuse.
What I can see is the case is that you're both way too confident in your inferences for a bunch of mind readers. Why not just call them up and find out? Oh right "not my job".
And btw "no X could be that Y" last time I heard that line was in a sitcom.
