I believe the poster was attempting to draw some connection between John 20:19 and the manner of Jesus birth when there is none.
Why would that be attempted? I must assume because of a tale even the Catholic Church recognizes as spurious is accepted as fact by the poster.
“The reason for the belief has to do with the supernatural nature of Incarnation and Resurrection as such”
Sounds more like getting lost in the jungles of speculative analogies and never finding the way out.
Very likely. Religions are prone to that, these threads being perfect examples of that.
But don't think the Protestants are not in it. Take for example Christmas being on December 25th? It ain't biblical but the Prots accept it. I have yet to read a Protestant thread that calls Christmas a spurious and a speculative date. :)