No, it is any inbound link to a page unlikely to be typed manually "blah.com/articles/random/crap/article-title-goes-here/35487623", that has no referrer header at all. Traffic coming from other websites will still have referrer headers, just traffic from email, IM, etc don't.
He did mention that, but of course there's no way to figure out how much of that traffic is from https referrals. Of course, I wouldn't be shocked if 90%+ of https referrals are from gmail, which would put it right back to what he is assuming: email, IM, etc.
