Why does Excel think CSV files are SYLK?
Why does Excel think CSV files are SYLK?
Your file probably starts with ID; or something similar.
If the first two characters of the file are uppercase ID Excel assumes it's an SYLK file type. If you want to keep the column name you can make the characters lower case or insert an apostrophe, ', as first character in a text editor before opening in Excel.
The problem goes back to at least Office 2003 and is still present in Office 2013.