What does 'its casual association with fun and sun' mean? I assume surfing is linked with fun and probably sun, not moon, but what does 'casual' mean in this context? I've looked up the word in the dictionaries, but I couldn't match it up with the right definition.
For some, it’s a serious sport. For others, just a way to let loose. But despite its casual association with fun and sun, surfing has a richer and deeper history than many realize. What we today call surfing originated in the Polynesian islands of the Pacific Ocean. We know from various accounts that wave riding was done throughout the Polynesian Pacific, as well as in West Africa and Peru.
source : The complicated history of surfing - Scott Laderman https://ed.ted.com/lessons/the-complicated-history-of-surfing-scott-laderman