It is important to note that this is a study of people who happened to be stronger, not people who were randomly caused to be stronger (ie by randomly assigning workout routines). Larry Wassermann has a great write up on the distinction with regards to inferring causation vs association here:

http://normaldeviate.wordpress.com/2012/06/18/48/

It is good that they attempted to control for things like cardiovascular fitness but on there are also confounding factors like genetics and selection bias that are harder to look at (ie maybe the genetic variants that make it easier to build fast twitch muscles are what has the protective effect and increased strength training won't help someone without those genes).

That being said I highly endorse bouldering and rock climbing in general as a way to build strength and move towards a healthy life style for people who don't enjoy typical gym workouts.