Complex sentence: Instead of being released under the Xbox name, the Xbox 360 was released (2005), and XNA came to stand for "XNA's Not Acronymed", which is true because XNA is an abbreviation, not an acronym.
Split into simpler sentences: Instead of being released under the Xbox name, the Xbox 360 was released (2005), and XNA came to stand for "XNA's Not Acronymed". XNA stands for "XNA's Not Acronymed", this is true because XNA is an abbreviation, not an acronym.