this tells me nothing about what the game will look like, or run like
I mean... This was the first trailer to stir up a bit of excitement for a game that has only just entered full-scale development. They probably don't even yet know themselves what it will look like and how it will run on what hardware. Expecting that kind of info at this point is unrealistic
It's about setting expectations. The wording is chosen because they believe that paying open source developers for their work should be the norm, not the exception. Calling it a donation would not do that justice. Their wording is saying "Here's the software, we'll trust you to pay us for it if it brings you value and you can afford it". It's an explicit expectation to pay, unless you have good reasons not to, which is also fine but should be the exception. Whereas a donation is very much optional and not the default expectation by nature.
In the end it's just a semantic difference, it's just all about making expectations clear even if there is no enforcement around them.