The gist summary on TFA says:
> even if you've disabled all use of Spotlight Suggestions and sharing of Usage and Diagnostics data
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praseodym is pointing out that there are two checkboxes called "Spotlight Suggestions". One in System Preferences, and one in Safari.
It's unclear which OP unchecked.
Screenshots of the two options: http://imgur.com/a/TWDxy
Had deleted my original comment because OP mentioned "all use of Spotlight Suggestions", so I assumed that OP did uncheck the Safari Preferences box. But apparently OP only unchecked the System Preferences one.
As noticed elsewhere in this HN thread (https://news.ycombinator.com/item?id=8480173), unchecking the Safari Preferences box fixes the issue.