I believe it is mostly speculation. There isn't a hard proof out there. However, it makes sense that this was the attitude of the Church back then as it piggybacks on the patriarchal Old Testament.
In "the olden days" women were sold to their husbands, husbands could buy and own multiple wives - not the other way around. Men could have their wives killed if they found they were not virgins after wedding/purchasing them. The reason it was so bad to sleep with an unmarried woman was because it was a disgrace to the father who would now not receive money/riches from selling his daughter to a husband.
When the Israelites went to attack other nations they were instructed to kill the men, mothers, and boys but check any attractive women and keep them for themselves if they were virgins. Imagine you being a woman in this time and a soldier comes in, kills your husband and throws you on the table and opens your dress to check if you are a "virgin", killing you if you are not.... And God was ok with, nay - he commanded this? *shudders* Women were booty, like cattle and food and riches..
For years Christianity has seen man as the head of the household - to this day some conservative churches still do not permit women to teach over a man at church or in the home. Fortunately Paul's ideas (if they were his) are much tamer than what they could have been considering the source.
So in closing I feel it is very likely that it is not a forgery, it seems to fit in with the general thought of the NT.
Eric