Why would Google rank a highly irrelevant page in the top 15 especially for a seemingly important keyword?

[suskanchan]

While searching for "Blog writing service reviews", I found that a web page that's not even optimized for the query is ranking within top 15 search results. Upon checking the source code, I found that the webpage has been optimized for product reviews services. Plus, the website is only 11 months old, got 7 digit Alexa rank and has PR 1. Why would Google rank such a page in top 15?

[KevinBudzynski]

Because the Google Algo placed it there. Often times for long-tail queries, the exact phrase does not show in order or does not have the exact wording. The page does have "blog writing service" and "review" on it and if you Googled "blog writing service reviews" with exact matching (quotes), only 3 results show. So Google will try to fill the results w/what they determine may be relevant to the user's query. Often times, it's not because of the exponentially high number of possible queries, it's difficult to always have exact matching results.

[David-Kley]

Sometimes its about what you cant see. Backlinks, and other sources may exist that factor into a higher ranking.