Why would you feel calm and comfortable from a sunset? Probably to get you sleepy so you go find a place to sleep since there isn't much useful to do at night. That would be unrelated to play.
Anyway, most of our feelings comes from nature, we didn't evolve to be faulty, we evolved to do things efficiently, play is a part of efficiency. If it isn't for learning you would have to explain what it is more likely to be for. When kittens play and chase things or play fight with each other, do you think they are just wasting energy for no reason? No, they sharpen their senses and learn to hunt and fight.