Jake & Amara got arrested for violation of Code Ten, Section 14. Operation of an unregistered Jaeger.
Why did they put people who are the opposite sex in the same cell?
This is a 'holding cell'. In many jurisdictions there are no specific laws that prevent people from being held with members of the opposite sex, especially when they're rated as being low risk of sexual offending.
Inside the holding cell, Jake and Amara waited for the PPDC. A tense silence grew between them.
For the record, International Building Regulations for court holding cells don't even specify that they should be segregated by gender or age, they only indicate that there should be at least one cell of each type that is accessible.