This is most likely cheating. Sometimes, disconnects do happen though, even while opponents are put to an expensive decision.
When this happens and it looks suspicious, I always report the table name, hand number, and offending party to alerts@partypoker.com. You should also CC
alerts@empirepoker.com as the sites share ring games.
Tell them that you find the play highly suspicious. Each time they have responded to me telling me that they will review the opponent's past disconnect history to find similar events. I have had them email me back and tell me they were suspending a person's disconnect protect, so that if it happens again the person's hand is folded.
Keep reporting these types... they will eventually get caught. If a person is reported enough, they will lose their disconnect protection (personally I think their account should be banned).
J.