I don't believe it. If that were the case, there would be no "regulars"...they'd just be called "left foot fowards". Regular means the standard or majority. Those stats were skewed, for whatever reason.
The name came around long before snowboarding was invented...
I did a bunch of digging but haven't found any studies to deny/confirm the allegations.
Every online poll that I found had the ratio at MOST 60/40 but in most cases very close to 50/50.