If you study the history of animation, you will be exposed to the work of Zagreb Studios. So if you're an animator it comes across as an inside joke, but to anyone else it's just a super-obscure reference.
For me personally, I spent most of the 70's bored to death in school, but I got to come home and watch shows like "International Animation Festival" on Channel 13 (PBS if you grew up in the NYC area). They also had the first run of Monty Python's Flying Circus in the US, which was one of the few things me and my dad enjoyed together.
But the bulk the animation shown on PBS came from the NFB - The National Film Board of Canada, which provided the retro aestheics that were later adopted by Boards of Canada.
https://youtu.be/zb0PA-TaS4g