He called his show the “show about nothing”, and Comedians in Cars Getting Coffee would pretty much also qualify for that title. It’s all 100% fluff. (I love his stuff for exactly that quality)
He most certainly did not, he specifically called it the opposite (see point 4): https://www.rollingstone.com/culture/culture-news/10-facts-a...
Calling it “about nothing” is a meme with no basis in reality. That misconception even came from an episode which is about pitching a show. Seinfeld episodes are so clearly about something; they hit you on the head with the theme right at the start of each episode.
He even references scenes that they do in Seinfeld when pitching it.
And I wouldn't call it fluff, its observational humor and his style is to do 95% detailed setup and a quick punchline connecting it altogether.