Bitcoin demonstrates the attributes of a currency, but its primary source of value lies in its restricted supply and increasing demand
Not restricted supply because the supply of bitcoin is not restricted. Or if you count the ones that have not been mined as restricted, they will still be mined. But the main reason the value of bitcoin increases that is leading to its increasing demand is the limited supply whichwill not be more than 21 million BTC. I think this is what you are referring to.