The @lazy-panda account has decided to take advantage of the lucrative 20% APR on HBD and stacked more than 600k HBD.
A few months back (October), this account was not in the top, so its a fresh addition. I waggly remember it has been in the lists, probably a bit lower, but obviously it has decided to up its game.
Probably it is not the single reason, but it can be a big contributor to the latest HBD/HIVE price action. The 20% APR is driving demand for HBD and HIVE.