During the interview, Lee noted that through 2018, the BMI has not been over 50, while it now recently touched a value of 89. According to Lee, values over 67 have never taken place in a bear market.
Firstly, we don't know what the BMI actually consists of. I believe that it's supposed to measure market sentiment, but there is absolutely no publicly available data to show that this index is actually accurate in performing that function.
As a result, you have this situation where an analyst is trying to analyse the market based on an index that is created by him, with no public credibility, and an uncertain track record. Also, as others have mentioned, Tom Lee has shown a blatant disregard for market conditions in the past in his analysis and is somewhat of a mainstream, sensationalist speculator more than anything else.
I'm not saying that his prediction wouldn't pan out, because I think that it's likely a bull market will emerge within this current decade. But the process he goes through to come to his predictions is questionable at best.