Alfie is little and fluffy. It's an easy enough mistake to make.
We adopted Mojo when she was between 4-6 months old. They had her listed as a boy, hense the name Mojo. In fact, the night we put in our application for her, they took her over to Banfield's to check if she was a girl, and if she had been spayed. Before they took her, she rolled on her back (when there was still a question), I looked at her and said, "Oh that is definitely a GIRL!"
But I guess all of the shelter workers had gone by her behavior and assumed she was a boy without actually looking.