@w3c Many people already pointed this out, but now you repeated this unfortunate phrasing, so it bears repeating:
For many people "X invented Y" implies that they were the sole inventor, rather than one of many. For the initial iteration of the Web, this is true for TBL, but no one person invented the internet.
The t-shirts in the initial post are of course entirely accurate and very funny, the explanation is potentially misleading.
EDIT: I noticed just now that the t-shirts in the video are not the same ones, so Cerf is actually wearing one that says "I invented the Internet" which I'm sure he himself wouldn't claim to have done, but he's being a good sport and indulging the joke.