If the original file was .mp3 format then that is what is downloaded to your device.
If you want to get the original file - you can also go to the RSS Feed for the show and find that episode and download it directly to your desktop.
To get the RSS feed for a podcast - search here - https://www.castfeedvalidator.com/FindCast.php
Then click "validate feed" for the show.
Then click "Start Validation"
Then click "See Preview"
Then find the episode in question and where it says "Play in new window" you can right click to choose to download the file.
Rob W