jQLite is a very stripped version on jQuery. jQLite is enough for angular to work. This is to remove any dependencies.
Yet, if you load jQuery before angular, then angular will use jQuery.
Most of the times, you do not need to use jQuery. Even so much that, for beginners, it is advised to leave out jQuery completely as there would be tendency to use jQuery when there is an easy / angular way. There has been so many examples on this (mostly showing and hiding element through jQuery when there is ngShow and ngHide directives).
Later on, when you start to write directives, you then may need to add jQuery.
ngGrid possible does so much things that which jqLite would not suffice. Thus, they used jQuery.
Documentation and features of jqLite: http://docs.angularjs.org/api/angular.element
jQuery vs. AngularJS: A Comparison and Migration Walkthrough
There was a time where it seemed like we barely even needed to talk about this: Joel had won the argument, the Internet agreed that private offices were the future, and only incompetent management or a tight budget was still putting developers in cubicle farms. A glorious future lay before us.