[Gigachad]

It's an open standard because the concepts and reference implementation are free and open source even if the PDF is paywalled. Realistically you could just pirate the PDF and write a jpeg xl encoder/decoder and your code wouldn't be infringing on any patents.

[201984]

Seems "closed but royalty free" would be a more accurate description then.

[Gigachad]

Splitting hairs on terminology I guess. Very few people are interested in the PDF that specifies the format vs being able to include decoders in software and on devices without paying a royalty for every device. There are alternative documents and the last draft copy which are free legally. As well as the reference code.

[ksec]

Before the world of internet, Open does not always mean free. They are two different concept. A proprietary codec isn't open, and you can't use it everywhere unless the owner allows you to or provided tools and support. Microsoft with their WMV and Realmedia with RVMB for example. H.263 and H.264 was called an open standard at the time, any body can buy and implement it.