That's pretty normal, though, and they're offering sell-to-cover as an option to their current employees, so that sale at the end of lock-up is going to happen regardless.

I'm not convinced these events represent a significant enough number of shares to move the price, though. And regardless, many current and former employees will use this opportunity to dump more shares than just to cover withholding. I wouldn't be surprised if the number of shares sold normally at that time will dwarf the number sold to cover tax withholding.