Zero is a privately held company, and it's the investors choice not to officially release sales numbers, so I'm not sure how this article got this information. It says "the company said" but I don't ever remember the company saying that in any press release or anything, and they don't name anyone from the company in that statement. Although since it wasn't contested by anyone, I guess the numbers could be a good ball park number.
I don't think there is any question that sales are going up every year with this year being a huge jump. While you might not be able to ask Zero directly, if you have followed Hollywood Electrics on social media the past few years, you notice they post photos of their new additions to the Hollywood Electrics family when an owner takes delivery of their new Zero. The frequency of these posts as been increasing each year. And this year was just wild! It seemed for a while this summer there were 2 or 3 new owners a week, sometimes it was every other day I felt. So for sure this year is their best ever for Hollywood Electrics. And since that is just one dealer, and the number of dealers has easily doubled or tripled or maybe more in the last two years if you look at the dealer map on the Zero webpage often. So if you do some simple math it's not hard to see the company is growing and demand for these bikes is increasing fast with this year growing at a higher number AND rate than the previous few years. I can only expect this to continue each year as the bikes go further for the same or less cost, and get better and more refined all around.