Key Confirmation Attack [Key Distribution Center (KDC)]
$ID_a, ID_b, ID_o$ are public information


Oscar sends to $KDC$ a legitimate (encrypted) request to communicate with Alice: $RQST(ID_o,ID_a)$
Oscar gets $Y_o, Y_a$
Oscar sends $Y_a, Y_o$ back to Alice. 


Alice cannot tell if she got $Y_b$ or $Y_o$, that's the problem. So, I would say the order of $ID_o$ and $ID_a$ are mixed up in the slide. It would be clearer if it was $RQST(ID_o, ID_a)$ instead of $RQST(ID_a, ID_o)$.