I'm sure it's all of their content plus half of the web. The proprietary data they get from Behance, Lightroom, Photoshop and Illustrator (and soon figma) has to be a great advantage for them though.
https://helpx.adobe.com/manage-account/using/machine-learnin...
"The insights obtained through content analysis will not be used to re-create your content or lead to identifying any personal information."