unfortunately doesn’t say anything about breathing through your nose versus mouth.
I think the technique is often described as inhaling through the nose and exhaling through the mouth, but please correct me if i’m wrong
Boxed breathing is just about the rhythm and can be done through the nose.
I've tried both (in resistance breathing you inhale, then exhale through pursed lips over a minute or so, repeat three times) - and they seem both to make me more relaxed and less anxious.