I'm not a doctor, but I have separated my own shoulder and seen separations on others. If it was out of the socket when he left the field, he would have been in much more pain and you would have seen the deformity right through his jersey. He said that he felt something move. When the shoulder pops out, you know exactly what happened and you can explain it better than "something moved". Based on that alone, I don't think he fully dislocated it. Of course, he is a pampered princess, so he'll miss 8 weeks.
Yaz might have missed the weekend. I hate today's overpaid pampered players. I lump them altogether, not singling out Ellsbury.