Mammal vs Placental Mammal
From the Tree of Life page for Mammalia:

 

All of these groups of animals are mammals, including extinct triconodonts and multituberculates. Among living mammals are monotremes (most notably the platypus), marsupials (kangaroos and opossums), and eutherians. Eutherians are placental mammals, so all eutherians are placental mammals, but not all mammals are eutherians.

Both armadillos and pangolins are eutherian mammals, so both are mammals and both are placentals. "Difference Between" is quite incorrect.