buckworks the logical of the theory is quite sound and it's not suggesting that you can't rank well on Poison Words > "search engines" and optimization would in this case be results 0 which isn't the case.
This is more to do with index results integrity. First this isn't a singling out of one site's performance > it's all sites therefore everyone is at the same disadvantage.
What it stops is "out of content" stuff, as an example:
Ford > massive site 10,000 pages > places a link to a search function upper left corner from all pages call search and they have an engine performance page targeting "performance optimization".
In addition there could be many external links call engine optimization pointing to this page.
The total site would be highly relevant to "search", and:
Based on the 10,000 search links and the engine and optimization in the page title, and external links for engine optimization they could easily rank #1 for search engine optimization... whereby they are totally irrelevant for the searching users query... poor quality results... SE users go elsewhere.
Poison Words are not Bad Words they just may be not relevant to the play of word in search results... I doubt Ford would intentional spam for search engine optimization but this could occur unless the integrity of the archive is protected.