Got it - so sounds like it is just pure supply and demand then. When it gets listed on exchange people holding the coin/token just come on and place sell orders and if people buy then that is the starting price and it just goes from there.
It's a free market so it's entirely supply and demand. There might be some market making at play depending on where they list. Sometimes the ICO must give up some coins to the exchange to allow them to market make. This means they'll put orders at either side of the order book but mostly they won't be filled.