because you could be a doctor on the phone, trying to understand if somebody is finally touching a girl who fell into a deep hole during an earthquake and must be sure... does he see her or is he touching her?
"He's touching her?" is arguably correct in everyday English if you have the right tone and pronunication, but Duolingo doesn't pay attention to punctuation in your answers. It can't tell the difference between "He's touching her?" and "He's touching her."