A stable currency is a tether, as well as a dollar. And bitcoin is really a speculative tool.
I would not bank on tether as a stable currency in any thing but name.
Bitcoin is of cause determined by market forces if demand and supply and such actions are influenced by a lot of factors.
I would not call this situation a massive crash but we are in territories we have not been in for a while.
I would expect corrections in the market soon.