Ice Floe is considered valid land for a hound attack to start.

Hounds aren't supposed to attack you when you're out at sea, only on solid land. However, the ice floe you fight the Frostjaw in is considered to be land rather than the floating sheet of ice that it is.

It leads to a pretty tricky situation since you'll likely be fighting a boss there and there's very little land to maneuver around on, which feels unintentional, so I thought I'd report it here.