Being let go during your probationary period for missing a day isn't uncommon. In 12 years of mfg, I have seen it dozens of times. Probationary periods are just that. Walk the tightest rope you can. Miss a day in your first three months, that supposedly gives them an idea of your work ethic (not saying I agree with that, just relaying what I have been told).

They could have just fired you over the phone, but some employers insist on face to face.