You could have just said cheap and or inexperienced. Adding “green card” and the part about not being from here adds a layer of political and racial under tone even though green card isn’t necessarily a race.
When they called me curry girl it was a racist remark even though curry is not a race.
Green card/implication of foreign labor does add an extra bit of information beyond just inexperience - it's that they are likely to be less acquainted with the laws/regulations which means they can be convinced to do illegal things and are less likely to know their rights and stand up to bad/illegal treatment by their employer.
When they called me curry girl it was a racist remark even though curry is not a race.