I think they were holding bitcoin on troubled day because they believe on the stability of digital currency in case of emergency. Since it is the first digital currency that we had most investors will be encourage on the safety that it brings than having an actual cash investments. In here your investment is safe once you know that you own account if fully secured. Currently it has a harder way to be hacked by other people unlik all those traditonal currencies where can be gone from us despite our refusal.