I didn't do anything special that I know of. I think it must be beginners luck! I have them in a Dixie cup with a sand peat mix sitting in water. The bench they're on is on the north facing side of the house so it doesn't get much sun.
They were started from gemmae not seed, maybe that's why? I did notice the ones I have in pure peat in a fish tank which has higher humidity sprouted a week sooner than these did. Maybe raise the humidity to get yours to sprout?