Its probably inflated, I had up to 3 devices streaming it upstairs TV, workshop TV, and then I use an old cell phone to stream stuff on WIFI onto my Bluetooth when I do yardwork. I also watched some from my cell phone while at the store so 4 different MAC addresses over the event. But I'm not going to sit in my living room for 8 hours watching skiing. I did have it up and running and listened to a bunch of it and then if something happened you hit rewind and watch it. But that means at times you should divide that number by 2 or 3 because I would imagine most of us did something similar.
But then again some people might have been at a ski lake and had one TV streaming and 20 people watching. So its hard to get the total number. TWBC probably has an idea how many unique viewers
Waterski needs a captive audience it needs to host events at sites that hold people the old Malibu open Veteran's park is a great example - been to their beer fest in that same park. They regularly sell it out at 5000 tickets. That's 5000 people milling about in the same park get the event back and then coordinate to have the event through the beer fest and do social media to reach those people.
Ski lakes are often also large fields with lots of parking things you could host there music festivals or events, car shows, motorcycle shows. What could the venues be used for to get people there. Imagine a large food truck event our local park district has those on thursday nights with usually 8-10 foot trucks and about 1000 people attend over the course of a few hours. If your lake is near enough to a population center can you use those food trucks and their media to draw people in If you're ski lake is in an area with great gravel roads or trails can you host a tough mudder event and have people start/finish at the lake with a ski event going on.
Venn diagram skiers, mountain bike enthusiasts, 5K runners, IPA drinkers, foot truck frequenters, classic car enthusiasts.
If you were doing social media and wanted to explode the exposure in terms of people who atleast watch a summary reel or check into it you have to not just be looking at the people who are already willing to go or watching TWBC you have to make reasons for people who normally wouldn't to check in on it.