It will rebound quickly. Someone sold 2 blocks or two trades equal to half the days total trading volume. A big holder just happened to want out just like you will want to sell some day for whatever reason. It will recover a lot of the drop just today before the close.
First, full disclosure, I am long SLP. While, as of this moment in time, it does appear that SLP is "valued" if not a bit over valued. The question is, where does it go from here? With almost $1 in cash, no debt, a very good dividend, growth in the company, massive growth in the industry...I, at least, feel this is a good recipe for good things in the future. I especially feel this way due to the nature of the company and the effect improvement in the industry will have.
I haven't seen any news. We've had a fairly strong price increase recently so it may just be a " reversion to the mean" type price move. Part of it may also be the fact that the dividend was paid this past Monday so there are probably some sellers that were waiting on the payout.