Heard on LiveATC that ATC wants to "cancel" something. What did the ATC mean by that?
If the airport is non-towered, then ATC may not be able to have radio contact with the aircraft after landing. However, the flight plan still needs to be cancelled or closed after landing. Usually this is done by the pilot calling ATC on the phone, but in this case it seems ATC offered to do it without the call.

Without closing the flight plan within approximately 30 minutes after the scheduled arrival time, the Flight Services will start looking for you. They will try to contact you by phone call and if that goes unanswered, eventually a search and rescue will be started. 

On ATC controlled airports the flight plan will automatically be closed after the aircraft landed.