First of all, I would like to praise the simplicity of the format of the story. The lay-out isn't messy and it fits the cover of the story. 

What I really liked about this story is that it isn't your typical cup of tea involving romance about the EXO members and throwing several ounces of fluff or angst here and there. What's awesome in Spontaneity is it tackles about a developmental disorder in order to spread awareness (that's what I supposed you meant in your author's note) and the fact that you didn't romanticize it. Any physical or mental disorder is a sensitive topic, and as I did a little bit of research about the disease Jongdae has, you didn't exaggerate any bit. Perhaps this was because you know someone who's suffering about it.

Then, I adore how you were able to create an entire story (although it's still the start of the two main character's friendship) by using only one scene. Jongdae has always been sitting on the bench alone and it was the missing screw that triggered his need to repair it. Then, he met Baekhyun who gave off a mysterious but friendly vibe. I like how their friendship wasn't forced and how understanding Baekhyun was. I'd presume he didn't know Jongdae was suffering from Asperger's, which makes Baekhyun more endearing. The icing of the cake was the moment Jongdae revealed his name to Baekhyun. It felt... rewarding, after all the things Baekhyun did for him. 

If I would to describe Spontaneity into an object, it'll be a chocolate drink. It's warm to your heart. Your vocabulary is also exceptional. The words you chose to describe every action and their conversation seemed natural. But, there were lots of grammar errors in your story. I also noticed that you tend to use run-on sentences a lot. 

This was found in your description:
"It wasn't until a chance encounter with a stranger named Byun Baekhyun that Jongdae learned change."
This can be:
"It wasn't until a chance encounter with a stranger named Byun Baekhyun that Jongdae learned to change." or "...learned what change is."

Certain typos:
"He had been told on multiple occasiona that would be strange."
Corrected:
"He had been told on multiple occasions that would be strange."

Then, if you write dialogues, the next action (especially if it's done by the other character) should be made into a new paragraph.
Yours: 
"Nope," Baekhyun says, popping the 'p' at the end of the worrd. Jongdae sighed and ate the last bit of his sandwich. He didn't understand where this conversation was going...
Corrected:
"Nope," Baekhyun says, popping the 'p' at the end of the word.
(Next paragraph)
Jongdae sighed and ate the last bit of his sandwich. He didn't understand where this conversation was going...

Therefore I suggest you to find a beta-reader if you haven't already. This was the only problem I found with your story which speaks a lot. A few changes here and there will fix this, and you'd be suited to enter the competition.