Understanding Dataweave for CSV input

Hi, 

I am learning Dataweave with the dataweave playground available online. 

There is a question that I want to ask and I include the screenshot below to better explain this: 

So, the left hand side, the data is 2 lines of CSV format: 

0088|12345 

0088|12345 

In the middle, on line 14, I try to splitBy the payload by '\n' 

In the right hand side, there is an error that I believe basically says I cannot split on an array argument  

[{"0088|12345": "0088|12345"}]

My question is, how the 2 lines of the CSV input can become Array format that if I interpret, it looks like a json object with field "0088|12345" (1st line) having the value of "0088|12345" (2nd line)? 

Thank you