Okay, I found a single use of "ambiguous topic" at WP:D, which is under WP:PRIMARYTOPIC. In that context, "...one of the ambiguous topics...", it's clear that it means any one of several topics which might be sought by entering the term in question in the search box. In that sense, clearly Tom Freston is an "ambiguous topic" of "Freston" as it is listed on the dab page for "Freston", not to mention because it is a topic likely to be searched for when someone enters "Freston" in the search box.
Because you think partial titles are relevant, I think you mean something else by "ambiguous topic", something like, "any topic which would use the term in question as its title if there were no other uses for that term". Since Tom Freston would never be at Freston and would always be at Tom Freston, you're saying it's not an "ambiguous topic", and therefore should not be considered in primary topic determination for "Freston" (please correct me if I'm wrong). Again, I suggest that there is no support for that narrow of a definition of "ambiguous topic" anywhere in WP:D, and ask you again to show us where it is in case I'm missing something.
If we did define "ambiguous topic" in terms of title, then it would be something like, "any topic which would use the term in question as its title or as a redirect to it if there were no other notable uses for it." Clearly, if there were no other uses, Freston would be a redirect to Tom Freston, as countless single-use surnames redirect to articles about people, like, for example, McNealy is a redirect to Scott McNealy, and Palmisano is a redirect to Samuel J. Palmisano. If there were small Scottish and Italian villages named "McNealy" and "Palmisano" respectively (or any other notable uses of these terms for that matter), then these would both be "ambiguous topics" for those two names, just as the topic of "Tom Freston" is an ambiguous topic of "Freston", and we would consider their relative likelihoods of being sought when readers enter those surnames in the search box (we wouldn't discount them simply because they are surnames or "partial titles"). --Born2cycle (talk) 17:36, 29 November 2010 (UTC)