Warning the disbelievers of the Quraysh for rejecting His Messenger Muhammad ﷺ, Allah says that He destroyed other nations who rejected the Messengers after Nuh. This indicates that during the centuries between Adam and Nuh, humans were following Islam, as Ibn `Abbas said: "Between Adam and Nuh there were ten generations, during all of which humans were following Islam." The meaning (of the Ayah) is: "You disbelievers are not more dear to Allah than they were, and you have rejected the most noble of the Messengers and the best of creation, so you are more deserving of punishment."
وَكَفَى بِرَبِّكَ بِذُنُوبِ عِبَادِهِ خَبِيرَا بَصِيرًا
(And sufficient is your Lord as All-Knower and Seer of the sins of His servants.) means, He knows everything they do, good and evil, and nothing at all is hidden from Him, may He be glorified and exalted.