Bombachas are traditional manly pants - they let a man's terstcles breathe and bob comfortably (ok, and also for a man to ride). That's why it'd be nonsense for women to wear it (women wore dresses).
So, there you go. "Gaucho pants" are the same as "bombachas". It's a man's clothing. The text is completely lacking the historical/cultural basis for this piece of clothing.
How do I know all of this? I'm Gaucho (that is, a Brazilian from the Rio Grande do Sul State, *bordering* Argentina - "gaucho" is our gentilic).