This could certainly be critical. Just a theory: Perhaps moving domains triggered a "recalculation" of the link values to the site, and he fell due to violations like this?
Or, more likely, the domain move triggered a manual review and somebody at Google didn't like this page.
I worked in SEO and talked to a guy who manually checked a lot of websites for google. This was a few years ago, but he implied that there was a small army of people manually checking websites.