Volla is just forwarding the trees made available by their upstream ODMs. E.g. Gigaset publishes them:

https://github.com/Gigaset-dev

I am not sure about the Daria Bond, but in Ubuntu Touch (which seems one of the very few Linux systems that supports the Daria Bond, ahem, Quintus), most of it seems to be the work of LineageOS developers (probably for generic Mediatek support, since it's a run-off-the-mill Mediatek phone), with some changes from Daria people on top of it.

So, I think you are giving credit to Volla that should go to the upstream ODMs and Lineage.

Or just go to the Volla about page:

https://volla.online/en/about/

It's just sales, marketing, and customer support people.