First part of my answer:
Cancel - Run or Run - Cancel?
There's always the debate on whether we should use Ok - Cancel or Cancel - Ok. In this post Rahul answered the question by stating research by Jakob Nielson. OK-Cancel or Cancel-OK?
Very very short answer:
Should the OK button come before or after the Cancel button? Following
platform conventions is more important than suboptimizing an
individual dialog box.
Ubuntu/Linux normally uses the Cancel - Ok version so that is probably the reason why the developer grouped them together like the example you gave.
Second part of my answer:
Why not put cancel on the left of the other buttons?
From a usability perspective it seems strange to put four different options in a dialog window. A dialog is normally used to answer a question with two possible answers, sometimes three. The more buttons you use, the more of a cognitive load you put on the user, and the more difficult it becomes to answer the question. So normally I would not look to improve this single dialog. Instead I would analyse the flow on how to get to this dialog and see whether we can reduce the number of options here.
Since we cannot tell why it is done like this. Not knowing the program, context, and it's developer. We cannot really answer your question. Yet based on what I'm seeing right now, 'Run in terminal' is an outlier option here since it doesn't answer the dialog window directly. It is a suboption of 'Run'.
In the dialog window the question is to select either 'Run' or 'Display'. From that perspective I would have suggested something in the line of Cancel - Run - Display.