Are you new to watching basketball? Rondo is right - transition offense starts on defense. Nine times out of 10, if a basket is made, the other team is going to get back. If the basket was a putback from an offensive rebound, you might have the opportunity to run because a couple players might be out of position, but only if your guys going for the rebound are able to recover more quickly. A couple times a game you might catch the other team napping and be able to push it from a miss, but you can't do it often, because they're not idiots. Furthermore, transition offense from a made basket typically requires a pass covering most of the court to take advantage of your player who got behind the defense --- these passes are quite risky and can lead to a turnover as much as a fast break.
When you get a rebound, on the other hand, you can start your transition faster. Rondo has known this his entire career -- it's why he gets rebounds, so he can push the basketball more quickly, as opposed to a big getting the rebound and looking to pass to Rondo, which slows your transition. It's one reason why Stevens wants multiple ball-handlers on the floor as well, so that there are multiple players who can start transition offense.
It goes the other way too -- a made basket helps set your defense too, so while good offense starts from an opponent's miss, good defense starts from your own make. This is partly why (in addition to randomness) basketball is often a game of runs. You make a basket, which helps your defense, causing the other guys to miss a basket, which gets you into your offense better, so you make a basket and repeat the cycle.