He didn't say that, he said the occasional bad link won't get your site flipped to supplemental or affect you being indexed in the main cache.
I would suggest he is referring to this meaning - conspicuously bad : FLAGRANT (again open to interpretation)
My take is that Google looks at sites in terms of a ratio of inbounds and outbounds as well as possibly the theme. I believe that the weight of too many links leaving the site ratio has a bigger impact than the relevance of the links, but do not have evidence.
Removing unrelated and poor links (links on FFA, bannable topics, more than 50 links per page, etc) simply increases your chance of having the BEST quality links to your website, which is always good.