Interesting that you got that boy out of that cross. The genetics aren't supposed to work that way unless your mutt meat girls had Cornish X or Ranger blood and was a dwarf herself. Breeding chickens reminds me of a song by Dickie Lee titled Laurie. One line in it is "strange things happen in this world".
Some strains of Cornish X and Rangers use dwarfism on the maternal side for certain benefits in feeding and management. I don't know which strains but dwarfism should only be carried by the boys when it is present. It is a sex linked recessive trait and can be hard to eliminate from the boys. Since it is sex linked it should be pretty obvious with the girls.
If you are going to mix a different chicken with a meat chicken, Ranger or Cornish X, it could be a reason to only use girls from the meat chickens. They should not have this gene.
Some strains of Cornish X and Rangers use dwarfism on the maternal side for certain benefits in feeding and management. I don't know which strains but dwarfism should only be carried by the boys when it is present. It is a sex linked recessive trait and can be hard to eliminate from the boys. Since it is sex linked it should be pretty obvious with the girls.
If you are going to mix a different chicken with a meat chicken, Ranger or Cornish X, it could be a reason to only use girls from the meat chickens. They should not have this gene.