On CNBC's "Halftime Report," Lamensdorf said that the bear case for some stocks remained intact.
"While we think a bounce is obviously occurring today and could go on for a few weeks, that was a super-negative hit that the market took," he said. "It created a lot of negative divergence."
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Among the ETF's short positions were such names as IBM, D.R. Horton, Harley-Davidson, MasterCard, Priceline, LinkedIn and Netflix.
This week, Netflix reported earnings in line with Wall Street estimates but fell short on its subscriber growth numbers.
Lamensdorf called the company "a disaster."
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"Fifty percent of the business is a DVD business that's going to zero," he said. "And the international Internet business growth that everyone's so excited about has yet to yield any cash flow at all. And the only reason that it's growing as fast as it's growing is because they're paying ridiculous amounts of money for content."
Lamensdorf said that Netflix would lose subscription growth "like crazy" if it tried to rein in content costs.
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"So, they're just overpaying, and they're not making any money at what they're doing," he said. "The earning quality's terrible."