Did you view the source of the document, are you sure it doesn't contain the term cat?
From the search results view the cache copy and also verify that it does not contain the term cat.
You may also want to check the query that was actually run change search.html to search.json, and look under response -> resultPacket -> queryAsProcessed, perhaps the query for cat was transformed into something else. Also check response -> resultPacket -> qsups.
externally the document could have cat assigned to it because of anchor text or from recorded click logs.
Perhaps this will help you:
-weight_only_fields=< S > Documents will not be retrieved in DAAT mode if they only match unfielded query
terms in one or more of the implicit fields listed here. For example,
specifying '[K,k]' will stop the query 'Monica Lewinski' matching a document
solely because of click data or referring anchortext.
you may also need to to set