Relative to software licenses, this would be the sort where the source code is there and you can read it, but that is all i.e. not Open Source nor Free Software.
It is not specified by a standards board or the like. It is an immutable protocol made by somebody's whim.
And it isn't very good. An example: It will never have a header with the size of the payload. The only way you will find out is by downloading the whole payload.
Gemini was first published roughly in 2019. At about three years old, what protocol has a standards board? It's too young.
It took C roughly 17 years to get a standards body.
It took Gopher three years to get the first RFC [1]. Was it a proprietary protocol? It was the same age as Gemini currently is.
[0] https://web.archive.org/web/20211026220037/https://lists.orb...
Your point is moot due to Gemini's immutability.
It isn't a protocol carefully designed by a committee. It is just somebody's brain fart. It cannot be fixed and we are giving it too much attention.