I'm not sure what "crowd" mean here.

Native speaker’s answer
Rebecca
In this context, "crowd" simply means people! A crowd is a large group of people, and it has been used casually here to emphasize the fact that 20 people is a large number. Ex: Wow, what a crowd! Let's avoid that part of the street. Ex: It's the usual crowd at the bar tonight. I love it when I recognize some familiar faces.