Don’t be frantic!!  Phenotype does not always match genotype in CAH.  This means that you can have mutations associated with non-saltwasting CAH, but present more like a salt-waster.  And vice versa.

Regardless of what mutations your son carries, if he had elevated potassium levels, your doctor was probably right to diagnose him as a salt-waster.  Treatment is based on symptoms and lab results, not what the genetics report says. 

I’m sure there are other conditions that can cause high potassium levels, but---assuming your son also had elevated 17-ohp (and possibly high renin and low sodium, to go with the elevated potassium)---it seems pretty certain that this is CAH, not anything else.  Especially since you also have confirmation of CAH genes, as icing on the cake.