That is more credible. A website extracting information about you from the DOM is a known threat: it's why CSS cannot apply all styles to visited links and why your browser will lie about the styles it can apply, to prevent websites from using JavaScript to determine what webpages you have visited from how the links are displayed. If you're using extensions that modify the DOM, like using an ad blocker to delete ad content, then that ad will still be missing when the website's own JavaScript goes looking for it.
That is more credible. A website extracting information about you from the DOM is a known threat: it's why CSS cannot apply all styles to visited links and why your browser will lie about the styles it can apply, to prevent websites from using JavaScript to determine what webpages you have visited from how the links are displayed. If you're using extensions that modify the DOM, like using an ad blocker to delete ad content, then that ad will still be missing when the website's own JavaScript goes looking for it.