|The content on your site (pages affected) may not fit a QDRL (query determines reading level) type filter or assessment. |
The content on your site may be totally unique, but you might not have been the 1st of say 10 to publish (or more importantly: get spidered) something similar (topically and informationally) out of all the pages GoogleBot has spidered.
The content (documents affected) may fit a classifier pattern of a 'spammy site' based on phrase frequency, related phrases, and 'natural language' factors. +(User Behavior and/or Links)?