when you search on some sites there are special urls that get cached.
someone can use these and index them i.e. pointing to a specific url.
some also use XSS bugs to inject html in the cached search results, but that is not allowed to talk about on this forum.
the sandbox is a myth and lots of people make up all kinds of theories about it.
i would check your on-page seo too and send more backlinks.
some mass sites perform better than others even if you duplicate 1:1 the same structure.
since google keeps indexing the pages, i would give it time as its...