he wouldn’t have been asked that if he hadn’t shown an email from ‘onward ticket dot com’ or whatever company he bought it from instead of the actual ticket.
On most Thai embassy sites they state exactly how much you need to show in either the local currency, or a currency they specify. When I was helping someone from the UK apply in Vietnam, the amount we used was over the ฿500,000 and we added a note showing the current exchange rate from GBP to baht on that day as we couldn’t expect Thai staff in a Vietnamese embassy to know the exchange rates for a multitude of currencies.
You cant go to the embassy or consulate. Everything is online.
They’ve clearly stated ‘not enough money’ so you’re going to need more.