This has to do with how Excel handles dates. If you copy that column and do "paste values", you will see the numbers that are being parsed.
So to solve this issue in Excel I have found a solution online that says to put an apostrophe in front of the date like so:
This tells Excel not to do that number formatting when copy, pasting, or when our system parses the spreadsheet.
If you dont feel like doing that, in Excel, you can go to File > Export > Change File Type > CSV. The CSV will have the correct date format automatically.