I believe you are referring to these instructions, right? Please note that these steps just describe one of the options for getting started with MEAN. You could use any alternative or variation of them according to your needs or experience.
Answering your question, yes, you may use npm instead to install the Angular CLI:
npm install -g @angular/cli
Then bootstrap your new project using the
ng tool that the Angular CLI provides:
ng new my-app
You can find more information about this in the official getting started guide.