That is true.
Why molds, to start with? After all, molds can be very expensive to make.
1) easier to make contours and complex shapes
2) more efficient and cost effective, in the long run
During the many years that I was a journeyman mold maker in the plastics industry, I made hundreds of expensive molds for many different types of molding (injection, transfer, compression, insert-molding, blow molding, etc.). Some vastly different approaches and processes, but all still bonafide molding.
Materials put into molds undergo physical and/or chemical changes that cause them to stay conformed to the shape of the mold.
My Winnie Drop roof is one-piece fiberglass, but it was not molded. While I am happy with the quality of the process used, and the quality of the camper, overall, I will admit that molded fiberglass campers use a superior process, in general. Lightweight and less likely to leak.