I would think it's because of an influx of new miners getting their rigs built, but that definitely seems like a huge increase of network hashrate.
Could be, could be not?
Geolocating the newly added nodes' ip address should be telling? Does anybody have that at hand? I know there were map implementations of that. If that can be combined with hash rate it will be really telling.
Luckily "other" showed up as less than 50% - for now that is. Until the geolocation of this new source of hash rate is known, and how dispersed it is, it will be a cause for concern.