Look at this visitor:
18.104.22.168 - - +0200 "GET /src/img/logo.png HTTP/1.1" 200 29349 "http://xxxxx.xxx/" "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/534+ (KHTML, like Gecko) BingPreview/1.0b"
The IP belongs MSN and the user agent turns out to be Bing Windows 8 app (http://www.bing.com/blogs/site_blogs/b/webmaster/archive/2012/10/26/page-snapshots-in-bing-windows-8-app-to-bring-new-crawl-traffic-to-sites.aspx). It loaded JS, CSS and images only, html was probably taken from Bing's index. The initial hit went to the preview image. It's a bit surprising that it triggered the JS tracker.
I suppose it should be reckoned as a bot, not as a visitor.
Keywords: bot, bing, preview
Piwik currently does not filter such requests. I'm currently implementing bot and other detections in DeviceDetector. Afterwards it might get implemented in Piwik.
For now you may try the third party plugin BotTracker.
In 63af7b0f316c316819ef28bcac5bd018c085632e: Fixes #5128 Count BingPreview as bot