Why did our bus driver do this?

When I was in first grade we went on a field trip to the aquarium and we had a really cool bus driver, she was blonde and she looked a little bit like Kim Wilde, on our bus ride to the aquarium she was so cool and would tell jokes but when we got back inside the bus after the trip she pretended like she didn’t know us and she was wearing a different shirt and she told us that she wasn’t the same bus driver and acts a little mean kind of like in a Cameron Diaz type of way. Why did she do this?