The file is a GIF because it's an old custom. Many of the younger members don't realise that in the earlier days of the Internet, PNG was not fully supported on Internet browsers and often had issues with Internet Explorer, that was one of the main used ones of the time. GIF, BMP and JPG were the big three image formats supported by most browsers and only one was suitable (BMP, the files were too big and as we know JPEGs ruin sprites). Only a few rippers still use GIF by choice. Of course it's still used in animations but that's down to the alternatives not getting used much.

Changing a GIF to a PNG wouldn't matter much.

okay, but, why's the file set to gif, and not png?
perhaps, if you change it.

thought he was hittin the caramelldansen

I wish this was expanded upon these amazing sprites.