Note how Solar didn't say the letter was EXACTLY the words of Guru, he said it was exact for the most part. In my opinion Sway doesn't seem too convinced about all this.

However at the same time, none of us know the true story behind all this. We don't know the real reason as to why Guru fell out with Premier. We also don't know for certain if Solar had a definite role in the Guru/Premier dilemma. Perhaps overtime more answers will be revealed to all this.