$ echo [1,2,"abc",4]
Output:
c
I came across this while trying to pass this string to my Node.js program as an argument. Instead Some weird Bash magic happened. I believe it is explained "somewhere" in lengthy man bash but I cannot find anything yet.
This is just a single character range glob written in a funny way.
[abc] matches one of the characters a, b or c.
[1,2,"abc",4] matches one of the characters a, b ,c,1,2,4 or comma, and is equivalent to [abc124,]
Since you have a directory named c, it matches and gets printed.