That’s actually a separate thing. I’ll try to give a high level of both.
RE: ember install, we encourage
ember install instead of
yarn/npm install because ember addons have these extra bits called blueprints which can do special stuff when installing e.g. add a new file to your project or run some other node code to configure the new addon. There’s nothing stopping you from using yarn or npm install commands, but sometimes you’ll then need to manually run the addon blueprint.