This was my first assumption(dirty competition). But keep in mind your site is not accessible unless you disable the extension. Traffic is redirected to https://metamask.io/phishing.html.

It seems the blacklist is updated via github https://github.com/409H/EtherAddressLookup. Though I couldn't see your url there when I took a quick look. Hopefully if you investigate more you'll be able to find the root cause.