"Why would longs blink"?
That is a good and reasonable question. Here are two possible answers:
1. Redemptions & portfolio re-balancing. If a Fidelity, etc., needs to cover for redemptions, it must sell something. Sometimes, their portfolio managers will shake out dogs to cover; sometimes big profitmakers. Also, portfolio mandates oft-times necessitate getting rid of at least some of a core holding: this fund can hold only X% in technology, Y% in automotive, Z% in US stocks, and so on.
2. As attractive as any particular name, let's call it "Tesla Motors" is, for a short-, medium-, or long-term perspective, there can come a time when something else seems to be particularly appealing. For example, exactly two years ago (1 August), for me Nvidia at $17.81 appeared to be fantastic. So I bought a bunch of it. IN RETROSPECT, I would have done far better - from the 5 August 2016 vantage point, mind you - had I then sold TSLA and bought 5Xabunch of it. So who knows what might pop up on the radar...or lidar...screen tomorrow that suggests it could share some TSLA shares from a hard-core long-term holder?
Anyway, there are two quasi-possible answers to your question.