I thought the Mike was always the second "LB" off the weakside (regardless of the player's actual position)? So in other words if a safety steps into the box at the WIL, then the WIL then becomes the Mike.
the MLB and the "mike" are not always synonymous
the only time they would be is if the MLB was the actual "free man"
they are not calling out the position ... they are calling out the man unaccounted for