On the one hand, it seems unlikely that an automated process would trigger external resource retrieval. In the same way, most processes that scan webpages for content or similarities don't run JavaScript, unless they are very sophisticated (this used to be a good way to protect against spam bots, for instance).

On the other hand, given how many files are uploaded to dropbox every hour, it's inconceivable that a human, whether through deliberate management direction or mischief, is opening all these documents. I would more concerned about human intervention if occasionally, a document triggered a buzz some days after it had been uploaded.

If all documents are showing as opened within 10 minutes, then surely it is just an anti-duplication automated agent at work.