I am the project lead of 300 BLK and gave him credit.
http://www.300aacblackout.com/resources/300-BLK.pdf
"Pioneering work by JD Jones with the 300 Whisper®, and others with 300 Fireball and 300-221, have proven the concept"
And on that note, the 300-221 concept has been out since at least 1969 - well before SSK/JD Jones helped make it popular. Look at page 11 of that presentation for photos from the 60s. Thirdly, the concept copied the case head dimensions, body taper, and case length of a Remington cartridge called the 221 Fireball. So everything was invented by Remington, except for the necking up to 30 caliber part - which is done to every cartridge made by someone.