Compromised private messages

I encountered a player that was aware of private messages to another player. His responses were so instantaneous I doubt my messages were passed along He claimed it was a bug in the system, but no other player was able to see private messages. Is this a "bug" or is there a spy upgrade that I haven't come across yet? Or were they simply two players in the same physical room.

1.- they may be in the same room
2.- the other person may told the other guy about your comments
3.- wrong chat.

Thanks for answer! If its not an upgrade then it must be number 1. I'm sure it was message right and his responses were so fast it didn't allow time to retype. OR 4th possibility - single person playing two profiles at same time as allies to double team although that would difficult...at least for me to do

Cheers

Cheers