It looks to me like the indicator has been above 2008 levels since 2014 and has been above 100% every year but one since 1998. The article doesn't give any kind of indication of what "too top-heavy" means, so it looks like they've picked a metric that has been above a threshold for a period of time that contained two market crashes, then just declared that said metric forecasts a worse crash.
The Buffett indicator may be worth paying attention to, and Buffett has certainly thought more about this than me. But given the data in the post, there's as much support for the record highs of the DJI warning of an impending stock crash as there is for the Buffett indicator.