Wherever I originate from, and I understand that the meaning is identical in Mexico, "chusma" is accustomed to make reference to "small class" people today. The top English equivalent I'm able to visualize is "riff-raff" Nos cuentas el origen de la expresión “dormir a pierna suelta” a quienes lo desconocíamos: https://beauemrva.blogunteer.com/32504863/the-smart-trick-of-chat-chusma-that-nobody-is-discussing