or something like that in the enclosing element, so it's not that they're inferring metadata from unstructured content - it's that they're drawing bad inferences from the metadata provided.
That said, inferring metadata from unstructured content is literally the whole goal of Reader mode - to make pages more readable even if the original source didn't design it to be - so while this particular bug is avoidable, others may not be.
There's no reliable way to do it. The right way would be to only use explicitly defined metadata and if it's not there to default to showing nothing.