Yes, that is correct. The html, css and js files are not part of Node-RED's flow, that is how uibuilder is designed. By keeping the files separate from the flow, you can use standard web development tools to manage your front-end code. This has a lot of benefits.
But it does mean that the examples require not only the flow to be imported but the front-end files to be edited. In the library and WIKI examples, I've generally put the custom code into comment nodes with a clear instruction that the contents have to be copied into the appropriate file.
From newer versions of uibuilder, it is now possible to have complete templates with all the files and folders needed in place. But not currently a flow, that is the subject of a future upgrade now that pluggable libraries are available in Node-RED. So eventually we will be able to have complete examples with both the flow and the template but at present that isn't possible.