Cubans have great defensive skills, this can be to the extreme, like Lara, which almost forgets the "hit" part of boxing and just avoids getting hit, making it a boring ass fight and allowing judges to find reasons to give the fight to the other fighter.
Rigo is a great example of what cuban boxing is at its best. Very fast, very technical, defense first but capitalizing in the opponents mistakes to land quick punches and then instantly go to defense again. Usually the defense is based on a lot of movement around the ring.
But they simply have some of the greatest boxers ever so you can't just peg it down to a few things, they also have one of the best heavyweights of all time.