It is quite the same thing I guess. You do skin fasting when your problem isn't getting any better despite all the products you use and if anything, it is becoming worse as your skin is overwhelmed. This is the time you might need to consider skin fasting or back to basic, by cutting out active ingredients and only using products for basic needs.
The first purpose is to calm your skin down because sometimes, unnecessary products are what causes unnecessary problems, despite what you might hear about various products and their claims. That's why we have to believe that our skin is already smart and knows what it needs, so we need to be more attentive towards its needs, which can be seen through various signs that appear on our skin.
I once did skin fasting when experiencing acne like never before. It helped a lot, as well as made me realize that minimalist was what I needed of a routine. It also made me realize the importance of keeping our skin hydrated.