Bootstrap is a very useful tool in some situations. As a developer with little to no graphic design ability (but a reasonable understanding of basic UI design), Bootstrap enables me to skip a massive chunk of work on projects that don't benefit from the attention of a designer (e.g. internal portals, administrative tools).

Is it a skill? No, it's a tool. Being able to use it involves some skill with HTML, CSS, and possibly Javascript.

Does it belong on a resume? Why not? At worst it may not be relevant to everything you might apply for; at best it shows a familiarity with available utilities that, required for a given project or not, might come in handy or at least show you're open to and have worked with current alternatives to the everything-from-scratch approach that's sometimes but not always necessary or helpful when developing for the web.

[edit] After going looking for an author citation, I see this is on the official blog of a digital agency, written by one of the partners, who refers to himself as a "titan of industry."

That's just embarrassing. The ego is stifling, and the tone screams "nightmarish to work for." [/edit]