Some time ago, when my wife got pregnant, she was let go from her job and they specifically told her it was because she was pregnant. She filed suit against them (ongoing) because they specifically said it was due to the pregnancy.
Sometimes companies do really shady stuff (like to my wife) and potentially hiring people for 4-month stints. Other times, they could just be using this as an "easier" way to fire someone - which is a bit passive aggressive.
I'll have to find out which it is in this case.