As far as I can tell the file name given to the deployment artifacts .bar or .jar is taken from the first .bpmn file found in the project. Is there any particular rationale to use this and not the project name?
Don't think there is a reasoning behind it. If I do need to make a guess: most of the times, you only have 1 process per deployment (unless you're using subprocesses etc). It makes sense to have the bar named after this process, in case you have multiple processes in your project.
It all depends on your deployment-needs, but most people use deployments with 1 or only a few processes in it… Feel free to rename the file, offcourse