From the plugin web page:
column separator
The plugin will read the first line of the file to count the occurrences of ,, \t, |, and ; as possible delimiters of columns. You can disable this auto-detection by passing the separator option.
In other words, by default the plugin will look for a number of separators other than comma as the column separator. If you don't want it to do this, use the separator parameter to specify the character that separates columns in your data. The main reason to override the separator is that your data contains one of the default characters and you don't want it to be interpreted as a column break.