The number itself is not enough to have the encoded information, you also need the details of the encoding/decoding scheme. So if you had this 'commentary on Shakespear' by itself it's no more interesting than if you had an encrypted copy of Bill's credit card number but not the password to unencrypt it. Having that on a T-Shirt doesn't seem quite so outrageous though.

However if you have, or circulate this number along with an implementation of the decoding algorithm, as a reader, then you're actually circulating the credit card number itself in a much more direct way. Yes, I know they also publish the unpacking algorithms, but If I walked round with a T-shirt with the encoded file on the front, and the decoding program on the back, that's clearly a much more direct and obvious transgression.

The joke about these illegal primes is that by themselves they seem innocuous, they're just seemingly meaningless numbers, but put the two halves of the puzzle together and the problem becomes a lot clearer. Handing out an unreadable, encrypted, encoded number with the latest Marvel movie in it but no way to play it seems harmless, hand it out with a bundled video player as well and that's a problem. Now it's a viewable movie and that's a different kettle of fish.

A friend of mine got very excited when we were CS students because he found a way to theoretically 'encrypt and compress' data to extremely small sizes, until I pointed out the binary compression key would end up being vastly bigger than the 'compressed' file. Basically he was just 'sucking' the complexity out of the data file and putting it in the key. These numbers are a bit like that, a large amount of the information in the 'encoded' content is actually sequestered in the unpacking algorithm.

With the right 'decoding scheme' the number 5 is an encoded copy of Infinity War. Wow, 5 is now an illegal prime!