Does a person know who is on the other end of a sending stone?

At the end of the last session my players took out an enemy NPC who was using a sending stone while on the lookout for the rest of the gang they are sneaking up on.

I am fully expecting them to try and use the stone to pretend all is well, my gut feeling is to allow it, it is a clever use of a simple magical item to throw the enemy off track.

However I just wanted to make sure that mechanically this makes sense, I am pretty sure a sending stone is not like a radio, you don’t hear the other persons voice. But would a wielder know someone different is on the other end or is this a DM decision thing?