Possibly, but the followup only tells us that, at least in the short term, kids will be less likely to delay gratification from specific individuals who have proven to be untrustworthy (and the protocol of that experiment kind of went for overkill on the "demonstrating untrustworthiness" angle.)

It might be that children become less able to delay gratification if raised in environments where they cannot trust promises from their guidance figures, but the same effect could very easily be caused by rational discounting of the value of promises from individuals who have proven unlikely to deliver on them.