I would like Kunal may overhear some of the conversation but CV's would not show him doing that just to torture us further. Sinal are always shown doing the wrong things at the wrong time.
Also another possibility is Witcha asking or pressuring Siddhi to be a witness in court , against her wishes as a plan [ She may tell Siddhi this way Kunal will be freed but her real plan would be to make Siddhi look more bad in eyes of Kunal in court]. Kunal as we know loves Siddhi and he would get angry and do something in court to lead us to that promo. This looks more of a possibility given the trend we have seen of Witcha's plans.
But as we all know, her plans backfire each time. But she is also a parallel lead , unfortunately for us, she will keep coming back with more plans