That's an issue with that page then. CB Activity will first attempt to parse metadata for media. If the page has poor metadata then it uses the first image it can find on the page. Below is the parsing it does. It starts from top to bottom so inline media being a last resort.
Code:
array( 'title' => array( '//meta[@name="og:title"]/@content',
'//meta[@name="twitter:title"]/@content',
'//meta[@name="title"]/@content',
'//meta[@property="og:title"]/@content',
'//meta[@property="twitter:title"]/@content',
'//meta[@property="title"]/@content',
'//title'
),
'description' => array( '//meta[@name="og:description"]/@content',
'//meta[@name="twitter:description"]/@content',
'//meta[@name="description"]/@content',
'//meta[@property="og:description"]/@content',
'//meta[@property="twitter:description"]/@content',
'//meta[@property="description"]/@content'
),
'media' => array( 'video' => array( '//meta[@name="og:video"]/@content',
'//meta[@name="og:video:url"]/@content',
'//meta[@name="twitter:player"]/@content',
'//meta[@property="og:video"]/@content',
'//meta[@property="og:video:url"]/@content',
'//meta[@property="twitter:player"]/@content',
'//video/@src'
),
'audio' => array( '//meta[@name="og:audio"]/@content',
'//meta[@name="og:audio:url"]/@content',
'//meta[@property="og:audio"]/@content',
'//meta[@property="og:audio:url"]/@content',
'//audio/@src'
),
'image' => array( '//meta[@name="og:image"]/@content',
'//meta[@name="og:image:url"]/@content',
'//meta[@name="twitter:image"]/@content',
'//meta[@name="image"]/@content',
'//meta[@property="og:image"]/@content',
'//meta[@property="og:image:url"]/@content',
'//meta[@property="twitter:image"]/@content',
'//meta[@property="image"]/@content',
'//img/@src'
)
)
);