No one said that, but the Konami Code is deeply engrained into the gaming psyche. Not many people can pull other cheat codes out of their hat on a whim
I'm unsure if Manic Miner's code is actually the first. It was the driver license number of the developer. But the Konami code is the most recognized, mainly because of Contra for the Famicom/NES.
The significance isn't how many games he worked, but the sheer number of gamers that memorized that sequence of button presses, testing them in every game imaginable to see if anything happened, Konami or not. Hell, Amazon Echo, Siri, and Google Home have preprogrammed lines if you verbally tell them the code. Just go to the Wikipedia page and you will find that quite a few websites have Konami code easter eggs, from World Wildlife Foundation to Buzzfeed. I remember the Palm Pre phone was rooted using the Konami code, albeit written out, but I thought that was the coolest thing in the world at the time, causing me to try the code out on everything I owned, from the TV remote to just about anything else with arrow keys, replacing the 'A', 'B', and 'Start' where necessary.
