Snowboarding is seen as such a fun activity, you might forget that it employs several compound movements and aerobic endurance while riding. Can snowboarding make you fit? If you snowboard enough, you will definitely notice a difference in your leg definition, strength and aerobic endurance.
With that said, it can also be seen as a physically demanding sport, especially as you progress into advanced and expert terrain. The strength, endurance, flexibility and muscle power needed to safely ride advanced terrain are as important as the self confidence you need to throw yourself into these extreme situations.