Complex sentence: According to Sheeren, he had initially played the guitar solo himself, but on listening to his recording, thought that it sounded like a "poor man's John Mayer", and as he knew Mayer, he contacted him to play the solo.
Split into simpler sentences: According to Sheeren, he had initially played the guitar solo himself, but on listening to his recording, thought that it sounded like a "poor man's John Mayer". As he knew Mayer, he contacted him to play the solo.