Opera Coast approaches safety differently from other browsers as it does not show overall encryption status separately, but considers it as part of a whole. For example, broken encryption is much worse if you are viewing your bank account than the website of a local restaurant.
Opera Coast will warn you when something happens that may try to deceive you or expose sensitive information. If your connection to your bank suddenly breaks or weakens, the app will step in and make sure you're aware of any potential danger.
In the particular case of filippo.io, Opera Coast interprets the page's security to be right between poor and good. The page loads untrusted elements, but it does not ask for a password or other sensitive information. If the page did ask for personal information, Opera Coast would warn you that it is not safe. Or, if the user came to this site from a trusted and safe source (i.e. not Google or other search engine), the app would also warn you.
We are continuously working on Opera Coast's security interpretations and will refrain from loading unsafe elements in future versions of the app.
I was perhaps a bit too quick, but I am glad you understood my cryptic answer.
If there are any other interested people my answer should have been:
The browser engine all third party browsers currently use on iOS is UIWebView. Since iOS 8, Safari uses WKWebView. They are quite similar, except for a few things, and one of those things is Indexed DB support.