Not entirely sure how big of a block you're referring to as I don't watch the tape, but my guess is that it was a trader or some PM who got out after making a quick buck. The stock was up ~15% for the week, so it's understandable how some folks want to take some chips off the table. It will be interesting to see if we keep up the momentum this coming week.
FWIW looks like the website now has pictures of the management team which is nice to see. I don't recall seeing that a week or so ago when I started my due diligence on the company.
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