simple, Teach was a poser!

From what I have been able to gather, Quench, Bellamy and Teach all used this or a similar design of this flag to attack, perhaps flying the Marblehead boys club flag? (sorry Tam, no reference)
The Quench trial was one of the first under the
1698 Piracy Act, extended with the 1700 statute. This enabled admirals to hold a court session, and to hear the trials of pirates in any place they deemed necessary, rather than requiring that the trial be held in England.
The trial was publicized as the first outside of Britain, but also by Britain as an example, in the attempt to quell their allies the Portuguese. Thus, the trial record had more exposure than what would be your average admiralty trial, and reportedly, the first trial of Judicial Murder in America.
Note: Both Larimore and Quench were targeting the Portuguese. Larimore was captured first, before Quench, but due to his service against the French and Spanish, was returned to England, and acquitted of the offenses against the Portuguese. Quench was made the example. Given the heightened exposure of this trial, I would assume it was extra detailed, and accurately recorded
This act was built upon, and to make corrections to the
Offences at Sea Act of 1536, which provided the death penalty for piracy offenses. (which 1536 act itself, was not appealed in its entirety until 1967!)
This statute also added the offence of being an accessory to piracy. Under the 1700 statute, any individual who may “knowingly or willingly … aid and assist, or maintain, procure, command, counsel, or advise” and persons to commit any act of piracy “shall be deemed and adjudged to be accessory to such piracy”. This title of accessory was also extended to any persons who “receive, entertain, or conceal any such pirate or robber”
These accessories “shall be enquired of, tried, heard, determined, and adjudged” following the statute of 1536 by Henry VIII and “shall suffer such pains of death” just as the pirates themselves would.
The majority of the cases tried under these admiralty courts followed the exact proceedings laid out in the 1700 statute. In addition, most pirates appeared to have been given a fair trial because, if the accused could not be confirmed to have taken part in the said piracy by witness testimony, they were often acquitted. However, in the admiralty court, murder was almost always considered the more serious charge. (1)
Hence the willingness of the crew to turn states evidence, and certainly expond on the use of the Old Roger, rather than flying the British standard.
It was not until the Piracy Act of 1837, that the death penalty was abolished for acts of Piracy.
(1)
Piracy Act of 1698
(2)
Offences of the Sea Act 1536