It would be nice if AWS provided mocks but the reality is that's there is more than one lib for creating stubs and mocks for every language. Additionally, I would assume that AWS want's to steer clear of making those types of decisions for the developer. The "what lib do I use for x" decisions that developers have to make.
Unit tests are all you should really need. Mock the AWS services and make sure to assert, where you can, the arguments being sent to those services and you should have enough coverage to get the job done.
My guess is that this was built for practice. That said, some of the data is coming back bad. The 'url' property contains an address that is missing the 'u' and 'a'. https://ghibliapi.herokpp.com
If used in the right context, I don't see a problem with 'zero rating.' T-mobile[0] has been doing this for a little bit now and, to me, it seems to be beneficial. The issues only arise when you are zero rating individual services belonging to one genre or vertical. Saying that Netflix won't count against your usage but Hulu does would be a problem.