just wait and see

Nothing anyone says is ever without a grain of truth. All jokes, lies and backhanded statements have a slight element of truth influencing the words said.
There needs to be motivation for someone to speak, whether from internal or external sources there is always a catalyst that causes you to say what you have said.
If something was to be completely untrue then it would be without a catalyst. It would be as if they had said something completely random for no reason at all. “Jokes” that supposedly have no truth behind them are within context however, they always fit into the natural flow of the conversation. Usually you can see what has been said or done that sparked their words but you need to look deeper into what internal forces have contributed.
After looking hard its usually obvious that, although tiny, their words are true (Even if they hardly believe it themselves).