ok was the new wtf croaking at all or was any of your existing wtf croaking.

if both were then it could turn out that you have 2 males which im not completely sure what they would do to each other.
i have played the croaking of a wtf to my frogs as i know i only have 1 male but he does play up and starts croaking back he has some times head butted the front glass of the tank.

if they didnt make any noises then are you sure that the frog wasnt just trying to see what it was you were doing or maybe it thought you had food.