You have a source to read that up? At least in 452, they (some) were already pretty sure about her being virgin.
Dioscorus then moved to depose Flavian of Constantinople and Eusebius of Dorylaeum on the grounds that they taught the Word had been made flesh and not just assumed flesh from the Virgin and that Christ had two natures.
https://en.m.wikipedia.org/wiki/Council_of_Chalcedon
Edit: the bible was written ca. 300 after christ tho. Probably because of this.
"Oh, no. Mah pants."