The author is actually a fairly well known adventure journalist and has written for a number of well known outdoor magazines/publications including Outside Magazine. I'm guessing he probably skis/rides and he probably has some decent connections in the adventure-sport world so I do not doubt the statistics he throws out.
Still, at the end of the day its pure speculation.
I can think of a number of reasons why the article might be true. Like the article says, snowboarding has always held a "younger" generation (no offense to the older guys on here, this is just a hypothesis). Would it be safe to say that over the last several years snowboarding has declined due to the economy falling out and younger people deciding to forego lift tickets, rentals, lessons, transportation costs, etc? Just an idea.