Something should be here?
Twitter Bootstrap is a front-end toolkit to rapidly build web applications.
Bootstrap is a framework that uses some of the latest browser techniques to provide you with stylish typography, navigation, buttons, tables, etc. One of the primary changes in Bootstrap 3 is an emphasis on Mobile-First responsive design. The goal is to elevate the mobile experience to a first-class citizen of the design process, because several billion mobile users is quite a large market to tap into. So, sites built with the current Bootstrap version target mobile devices and scale for larger screens depending on screen size.
We leave this as an exercise for you to figure out on your own.
The person that told you that is definitely a liar.
(Please identify them to us post haste.)