how did i get a card from someone that sent me one in massachusetts but it wasnt the post office that delivered it?

one of the newsletters likes to advertise people's birthdays, i got one from MA and it looked like the post office already stamped it but it wasnt them that delivered it, i heard some lady gave it to my manager with a small cake from safeway, i never got to see the person that delivered it and i doubt mail people go to safeway, so how did it get to me if i didnt get the card in my mailbox, how did the person get my card if it was supposed to go to my mailbox. just wondered how they did all that.my manager gave it to me with the cake from safeway.