tl;dr, as I understand it: when family members Like your Facebook content in relative quick succession, FB apparently interprets it as a signal that it is family-specific content. I didn't see any metrics but this seems plausible.

I think I'm more of a fan of FB than the average web geek, probably because I used it at its phase of peak innocence (college years) and have since weaned myself off to the point of checking it on a less-than-weekly basis. I also almost never post professional work there, nor "friend" current colleagues. Moreover, I've actively avoided declaring familial relationships (though I have listed a few fake relationships just to screw with the algorithm). But wasn't the feature of making yourself a "brand page" and/or having "subscribers" (which don't count toward the 5,000 friend limit) supposed to mitigate this a bit? I guess I'm so used to keeping Facebook solely for personal content (and using Twitter for public-facing content) that I'm out of touch with the sharing mechanics. That, and anecdotal experience of how baby/wedding pics seems to be the most Liked/Shared content in my friend network.