Even though the Romance Dawn special isn’t definitively One Piece, that punch is definitively Luffy.
In the Romance Dawn special, Luffy is taking on Spiel, a colorful pirate with the ability to use magic.
We also see it in the recent Romance Dawn anime special, which, while not canon One Piece, is based on the Romance Dawn one shot manga which displayed a lot of the ideas that OP creator Eiichiro Oda was working with before he truly nailed down his masterpiece.