This was before the document had been sent to anyone. It was still being edited, only my friend and I were working on it. Also, the documents were not public.
I would be surprised if Microsoft is intentionally indexing links in private documents, but my point stands: Google et al are remarkably good at indexing the web. If you don't want an otherwise public URL indexed you must use robots.txt or equivalent.
Either way, all publicly accesible documents will get indexed sooner or later.