As far as the raccoon goes, there really isn't a whole lot out of the ordinary taking place in this story. It's basically a raccoon doing raccoon things.
Raccoons are inquisitive animals and very capable climbers. While I've never seen one climbing a skyscraper, I've regularly spotted them climbing or on upper areas of multistory buildings. Raccoons, especially smaller onces, can climb on brick walls like they're walking across flat ground.
Raccoons are notorious for taking up residence in homes' attic spaces. We're never going to know exactly why it climbed the building, but the critters regularly explore around and look for food, and this one happened to try exploring a skyscraper. Raccoons need to eat, they need to nest, they need to avoid predators, such as coyotes and humans. Perhaps the building's dumpsters were fiercely guarded by a larger rival.
The only somewhat out of the ordinary aspect is that the raccoon was observed in the daytime, as they are normally nocturnal. However, it's not that far out of the ordinary, as raccoons are well adapted to urban areas, and their biological rhythms can change to be more suitable for an urban existence.
This story is really a study in viral media rather than anything to do with raccoons. An animal that happens to look cute just happened to be doing this at a time where someone saw it, where they just happened to take a picture and post it on the internet, and that posting just happened to be seen by someone who just happened to have wider connections to make it onto the news, and so on.
Because raccoons are cute and mischievous, but are not very often seen, it seems as though they regularly pop up in funny news story, such as when a subway line was shut down after a raccoon casually boarded the train, or more sadly when people found it funny to make a memorial to a raccoon's corpse after it laid on the sidewalk for a day.