Breathability is a spectrum and sadly to some extent it's down to washability, the more washable the less breathable a paint is likely to be. The chalky emulsion is probably equivalent to a 'flat matt' emulsion (see F&B Estate Emulsion) which is on the 'might be a bit wipeable at a pinch' end of the spectrum. I rate that as 'breathable' and have used it successfully on walls in a basement.
There's little on the Sanderson's website to guide anyone beyond marketing hype about some lovely colours - make of that what you will!
Entirely depends on SD value, nothing was forthcoming on the descriptions on their website so difficult to say if breathable or not.
Perhaps they might offer this info if you email them?