Apparently the current daily bitcoin trading volume is about 800k btc so theoretically if they sell their 100k btc within a couple of weeks for example, it shouldn't be noticeable.
I am more of the opinion that big institutions only give out news of when they are buying but only after that and they do not give out the news of when they are selling unless they have a reason to. They are more likely to sell of in portions slowly as the market rises after the news hits. They are in it for the profit and they know how to make it. Older bitcoin traders who have been watching the market have already figured this out.
Of course as long as the desired profit is crossed they will continue to FOMO the newbies into buying more and then wait for the crash to happen once again.