Thats some new bullshit theory and no it doesent fit me and people who i have observed irl showing their shadow, its clearly inferior that it comes out the most and also through tert but not as much as the inferior. What people say on the internets i cant count because i cant know whether they even know what they are talking about when it comes to typology(also many prove themselves wrong with stuff like 8 function theory).
Shadow means the undesired
traits in you that your ego wants to reject and not want to see as part of the self, stuff that is incompatible in this way with your ego(which with INFJ consists mostly of Ni and Fe if we leave other stuff out that isnt related to typology).
If you are an INFJ, i could make an assumption that you get obsessed with details(for example all the things that are wrong) and to some degree subjective logic(what the thing is that is wrong) and analyze all of it to quite a degree when you are pissed off to the point that you start to show some undesired traits of yours(shadow comes out).
Ps.
Lectures on Jung's Typology (Seminar Series): Marie-Louise von Franz, James Hillman: 9780882141046: Amazon.com: Books