My memory was that the farm dogs were excluded from the rebellion because they were considered too close to the humans. But I just looked up a plot summary and it talks about “Napoleon’s dogs” repeatedly as enforcers.
Anyway, what had the pig just told the dog that needed this interruption?
To me this is an undecidable, but it’s not of the “What in the world?” type, but just which of a few basic alternatives. It could be the speaker is right, and the particular paintings in this gallery are setting the kid off. Or the kid is just tired and cranky, and being still walking around anywhere in the museum would set off the tantrum. In which case the speaker is probably just dense and mistaken (and we’re amused at him); or he is attempting a joke of his own.