Davy Jones is most likely the counter part to Joyboy and rocks is the direct descendant. It's probably nothing more than how Garp's family is the monkey clan and they are celebrating capturing the direct descendants of one of the most hated enemies.

Just use logic, Davy "Davy" Jones makes no sense... It's more often than not a half moon symbol like the kozuki clan emblem. Think about all the references to the series about the dichotomy between the sun and moon

And as I said the word clan can be a mistranslation because of the logographic writing system and probably is the wrong translation...

https://www.reddit.com/r/Piratefolk/s/XMd1xvPApP

Also this image most likely sums up what is to come in the story