Java ferns reproduce that way under just about any conditions - not particularly in response to any lack of nutrients. You'd have to really work at it to starve a java fern, if there's fish food going into the tank and a window providing ambient light, there's bound to be enough nutrients for the fern to grow and multiply.
In any case, it's always fun to see plants multiply. Once the plantlets get big enough, you can break them off and tie them to pebbles or other pieces of driftwood.
Given some time, you'll get a whole bunch of bigger java ferns.