How is that not accurate? Renting out a room for someone to live in is legal but in some places it isn't illegal to do so without the proper zoning and/or permits. Therefore you would call someone doing that "illegally renting".
Because "enslaving" refers to the action of making someone a slave, not to the action of shipping someone who was already a slave to a new location. That's "illegally shipped", not "illegally enslaved".
Agreed on this point, although I also find the terminology of "legally enslaved" to be poor as I'm sure the enslaved people themselves did not give credence to that law.