I believe First Pirate means Joy Boy was First to give Meaning to a Flag that isn't associated with any Island or Kingdom or Goal
A Sea Symbol or Symbol of Freedom, something that Hiriluk Explained
In our History, First Pirate Flag Witnessed was described as "Black Flag with Crossbones, Death's Head & an Hourglass"
So Skull is obviously Reference to "Death" & Hourglass is Reference to saying to your Enemy "Your Time is almost Up"
If Joy Boy's Flag gonna be the Same, then that means his Enemy was Death & He Escaped Death then Conquered it which is what gave meaning to his Flag, and if even Death doesn't Stop you, then you basically inspire Hope to achieve anything, achieve the Impossible, which is what Hiriluk said about Pirate Flag
What about the Straw Hat or anything Symbolic added to the Flag? It represents what helped Joy Boy Defeat Death,
As Hiriluk's Flag had Sakura Petals, which is based on Story He told about Man who got Cured after finding Sakura Trees (Probably Him)
And this isn't Random, Oda did indeed Introduce Death Entity in Wano Arc
And entire One Piece Story is Heavily Inspired by Movie "The Adventures of Baron Munchausen"
Basically about a Man who decided to go on a Journey to save his Kingdom from an Invading Force
And throughout entire Journey, He was always Chased by Death, and He always manages to Escape
And at the End of Movie, all that He (Baron) Left for the People was a Tale
I believe Baron Munchausen = Joy Boy
Hiriluk's Death Chapter was Named "Snowy Tale" btw
And Drum Island Kingdom was later Named "Sakura Kingdom" after Hiriluk's Dream was Fulfilled & Wapol was Defeated
His Dream was Fulfilled by turning Snow to look like Cherry Blossoms (Cuz Sakura Trees can't grow in Snow)
This means that Ancient Kingdom is a Place Full of Laughter, just like Jaya is Depicted or Yasuie's Town
And Joy Boy's Journey ended with him discovering something that Defied Death
Whatever it was, it wasn't possible to be Created where there is Laughter (Mockery)
Joy Boy's Dream was to turn Laughter into this Death-Defying Treasure, something He Discovered but didn't Activate Unfortunately.
This is why many Characters Laugh or Smile when They are facing Death, it's all Reference to Joy Boy's Dream
As long as People Laugh, Death can't get to them (Something that was also seen in Baron Munchausen Movie)