That is the way I understood it as well. While it is true that some Rishonim say that they are created from sweat, the Gemara does not say that.
The Gemara actually says elsewhere (BB 74b) that everything in this world comes from male and female. The Zohar Hakadosh also says this. This Gemara can parallel the Sugya in Chulin where we say Minei Kagavli, that it grew only from the fish. We apply this to an animal that is nursing, as well.
I said earlier that we shouldn’t say about Chazal what they didn’t say about themselves. They tell us that their Mekor is from the Mishna or Braysa and Masa Umatan. They never quote outside sources or went to ask unless it was for a timely issue. The Sugya in Pesachim, on Amud Aleph, is a very good example of that; one Braysa after the next. We often see how Rav Popa or other Amoraim derive anatomy or other facts from the Mishna. The Tannaim themselves had a big Mesorah of Halachos, and some where able to Darshen certain facts from the Torah, too.
The Rishonim clearly quote outside sources and are therefore limited to that. And yet, we still know that since it is written with Ruach Hakodesh, although they assumed certain facts that they heard, we can often find the truth from within their words.
There is therefore a very big difference between the words of Chazal, who were actually careful not to accept what they heard, and the later generations when they had to turn to outside sources, as the Rambam writes.