if the vast majority of links are dofollow, does a site with a 50% nofollow profile appear normal? No. It is abnormal.
Ok first of all that clip is fairly old and was released I think around the time NF was not well understood.
Then to give you an example, I post in some forums so say I have 10,000 posts, the admin decides to change the forum layout and include member signatures with each post with the NF attribute. That gives in a second 10,000 NF links which is abnormal but can happen. Also several CMS apps changed the way they exposed links with NF in a single version update thus you have way more NFs than when Matt did the clip.
And in the meantime google changed the way it processes NFs and distributes rank internally in a site. I do not have details as you need to access their code to really know what's going on, but I won't be surprised if the internal rank flow distribution is significantly different now because of the NFs.
but it does not stop trust and relevancy and those are influential in rankings.
As far I can tell it does stop them, what else it does that's the thing. Nofollow it's not literally do not follow, so if you create an orphan page nobody knows about and link it externally or internally with NF, I am certain google will index it and return results from that page's keywords. Now what it will do with competition is another thing. And so to be on the safe side if I do not want to hard-link a page (eg: login) but still have it for visitors I use some js or a post form instead of the questionable NF.