I don’t think that necessarily makes it legal - they might be liable for "contributory copyright infringement”, which occurs if you deliberately and knowingly link to copyrighted materials and encourage/enable others to infringe.
To be honest I didn't see where the author was and wanted to provide a detailed example (I'm in the UK, but could post similar case results here, but this site has lots of US readers so thought that would clarify the legality for most people)
The main reason for the post is that your original post which implied that just because it didn't host the copyrighted content itself made it OK from a legal perspective - this is probably untrue.
One similar ruling for the ECJ is below, which again demonstrates that this would likely be illegal in Croatia:
As a further note, not only is the application itself probably illegal to develop / release, it is almost certainly illegal to use. It's unlikely to be the subject of enforcement action though for the users (Although I would be surprised if Viacom was cool with this).
It's a client, none of the copyrighted work is stored in the software, it merely facilitates the user to load it in a media player.
> Where is it sourcing the episodes from?
The answer is in the source: https://github.com/trakBan/spongebob-cli/blob/eac7eded094a48...
TLDR: seems to be fetched from a source called "megacartoons".