What happened to Dr Kaito?

Sabrina was talking to Dr Kaito when he exclaimed "who are you?" in surprise and his line was cut off suddenly. The line went dead. Sabrina stared at her phone. What happened? She checked her line. The bars were full. Maybe his phone ran out of battery?

She tried calling him back just to find out if anything was wrong. 

"The number you have dialled is not in service" came an automated voice. She frowned at her phone till Kavan asked her if everything was alright. 

"It is strange, we were talking and in the middle of the conversation, his line got cut off," she told Kavan. Kavan didn't seem worried. 

"Maybe his battery died?" he suggested. 

"That's what I thought too…but he shouted 'who are you' before the line was cut off, as if someone suddenly went up to him and surprised him," she said.