That is crazy!
I'm trying to think of the scenario for this. Since bitcoin was about $30 at the end of February, a crash to the $50s would only impact those who bought in March and early April. Those into both bitcoin and gold are probably not the kind to be leveraged much and there aren't many ways to obtain leverage with Bitcoin to begin with.
So the price of Bitcoin reverses and the person now has less net wealth, sells some gold to raise cash as previous cushion went into bitcoins? I'm having a hard time seeing that happen to any significant degree. But if Jim Rogers is talking about this there must be some of it happening that he knows of.
Now if he instead had said about rotation from gold to bitcoins, then that is something I'ld believe. Like how some amount of money that used to go into gold is now going into bitcoins instead. And without that buying of gold there was nothing else to hold the price of gold up against those shorting it.