It's actually not that. Spacing a header equally between preceding and following paragraphs can work fine. There's an obvious association with the following paragraph, because headers are expected to come before content, and so you don't need to imply that association visually.
In this case, the header is closer to the preceding paragraph (~15px) than to the following paragraph (~19px). It's visually implying a connection that doesn't exist, which is why it's problematic.
I think this highlights something that is missing from the article. That is, the importance of hierarchy. Colour, contrast, position and weight (ie. 'boldness') are all highly important in communicating the order of importance. One should be able to squint a distance away from the page and know instantly where the most important elements are.