There's truth to this. There's no "reason" bitcoin has to be valued high, it's just up to what folks are willing to pay for it. Folks are just gambling that the long term value is high.
now 12.5 million coins (give or take a few) for 6/7 billion earthlings = scarcity
according to the of economics, this makes bitcoin rare and therefore valuable. How valuable will depend on its ubiquity.
Scarcity does not, by itself, mean something will be valuable. It must also be desirable, and that is rather hard to predict.