Here’s what happens to traffic on your semi-moribund Tumblr page when daringfireball.net posts a link to your post about daringfireball.net.
Over the years at work, I’ve had my stuff linked to from several of the most-circulated U.S. newspapers’ and TV networks’ sites. When that happens, it’s normal to expect traffic to jump by about 3,000-4,000 visits. Never 20,000. Never even close.