Yes, it is. Using a library is a transition of abstraction layers. It's expected that some understanding might get lost at that point. It's also expected that you understand what the library promises to do when you make that call - i.e. that you read the docs.

Copy/paste lives at the same abstraction layer as code that you actually write yourself - the same level of understanding should apply. (Of course, if you don't understand any of the code you write, you're in the clear ;)