There is nothing malicious going on there. It does that so you can get instant answers where there would normally be auto-completion. This is covered very nicely in a paragraph in the addon's description, and can very obviously be disabled in the addon's preferences.
If you check the chrome page on fixtracking.com (prepared by DuckDuckGo), it is asking you to uncheck "Use a prediction service to help complete searches and URLs typed in the address bar", so what is the point here?It is enabled by default.
Not sure what you mean there -- these are two completely different things. That disables using a service (Google or Bing) to autocomplete. It does not affect what extensions like the DuckDuckGo one do.
