Well, somebody decided to give up on Cavium Networks (CAVM) today, apparently.

The company, which makes processors used by networking equipment companies like Cisco (CSCO), Juniper (JNPR), Huawei and others, has been growing rapidly. Lehman’s Tim Luke, who wrote a bullish note on the company today following a meeting with management in New York yesterday, expects the company to grow the top line 70% this year and 46% in 2009; he sees profits jumping to 42 cents this year and 70 cents next year from 6 cents last year, and says the company should grow 45-50% a year for the next 3-5 years. He says the company is seeing design win momentum, and expects the March quarter to be “solidly in line.” Luke today repeated his Overweight rating and $28 price target on the stock.

Nonetheless, the stock sold off today on big volume: CAVM lost $3.58, or 20.1%, to $14.22 (The stock has rebounded 81 cents in after hours trading.)

In an interview, Luke says he isn’t sure why the stock crumbled today; one possibility, he says, is that the final batch of about 3 million shares held by the company’s original venture investors could have been distributed to the VC’s limited partners. Volume in the stock today hit 3 million shares, or about 7.6% of the company’s shares outstanding. That the heaviest day of trading in the stock ever, other than the day it came public.

Thoughts, anyone?