Lower Block Lane Violation??

[CDurham]

Had a fellow official tell me of a play they had in their game. He is Trail and his partner is Lead during a 2 shot free throw. Team A is shooting a free throw and the Lead doesn't realize that a Team A player is occupying the lower block instead of a Team B player. He blows his whistle and calls a lane violation on Team A. Is this correct? Would you call this or step in and correct it?

Thanks