He runs a concentrated book and presumably must have got caught by the commodity correction.
Traders & investors usually are either good at timing, or playing themes longer-term. It is very rare for someone to be able to play a theme for months/years, AND then be able to spot the key reversals (out of the dozens of pullbacks that then get erased soon after). So with a thematic investor like Heebner, the major sector rotation turning points are almost always going to cause problems.
Basically there is a trade-off between having the conviction necessary to buy & hold a boom sector during its bull run, and the flexibility necessary to be able to exit and reverse when the bull run hits an inflection point and comes to an end. The more flexible trader will avoid the brutal drawdowns on trend reversal, but will not make as much money while the trend is running. The conviction trader will score big during the trend, and get hammered when it ends.