First of all, I'd like to point out the solid work that Jess Camerato is doing over on CSNNE. She has a talent for getting past the static basketball questions and getting to know players and bringing that understanding to the reader. Good stuff.
Bradley and Green became close friends last season on the Celtics. When Lee joined the team during the summer, they instantly clicked with him. They shared similar tastes in music and mutual character traits -- "cool," "goofy," "laid-back," they listed. (Leandro Barbosa, who signed in October, was also part of the crew until suffering a season-ending ACL injury and being traded in February.)
Rajon Rondo is also mentioned in that group. If you toss in Jared Sullinger (who's kind of out of sight out of mind at the moment) and you are looking at the core of the post-KG/Pierce era Celtics (barring trades). That doesn't guarantee on-court success, but it sure doesn't hurt. Great to hear that these guys are getting along and growing up and doing life together.