Greens emergence were a couple of different things.
1. Yes, Rondo did limit Green. With Rondo on the court (95% of the time), Green was relegated to spot up shooter. Green can shoot, but he's not a spot up shooter. He's a slasher who can shoot. On top of this, a lot of Greens' shots consisted of Rondo dribbling at the top of the key for 20 of the 24 seconds, then frantically passing it to Green who had to take a desperation, fadeaway, contested, 3 pointer. It's impossible to get into a rhythm and develop confidence like that. This is what the same problem with Terry was. Rondo's ball hogging completely wasted their talents.
2. Green is getting healthier. He is STILL not at 100% and has said so in interviews. I remember in the commentary of a game in the beginning of March (Heat??) it was said how Green's doctor said he wouldn't be able to play basketball until March of this year. Well guess when Green started going completely berserk? March. The beginning of the year he was still trying to recover. Now he can focus more on playing.
3. Fast break opportunities. Every single time we got a rebound, the ball would immediately go to Rondo, which in essence killed the fast break before it even started most of the time. Green gets a couple buckets or an assist or two a night just from outlets on the fast break. Those opportunities weren't there with Rondo who single handedly killed our fast break.
4. Confidence. This ties into his health, and the shots he's getting, but he obviously feels much more comfortable now. He's getting good looks and that in turn is helping him out on his 3 point range.
5. Hard work. His game has improved within the course of the season. He is shooting 3s not just from the corner now. He's added an impressive pull up mid range jumper which helps when defenders over commit to protecting the rim, and his left hand has improved a lot and he's added a cross over.