How did Petruchio have more proof of katharine's change when they met an old man on their way?

In scene five, Kate and Petruchio are on the road to Padua again. Petruchio continues his shrewish behavior, insisting that the sun is the moon and threatening to turn the cart around if Kate doesn't agree. Kate finally begins to play along, agreeing that the sun is the moon and then changing her opinion when Petruchio changes his. This game is interrupted by the appearance of the real Vincentio, Lucentio's father, whom Petruchio refers to as a "gentlewoman" (4.5: 29); he insists that Kate agree, and she does so, calling him a "budding virgin."