It doesn't prove it but it's a plausible theory that someone has figured out how run the steemd program on a GPU and is now running it on a powerful GPU rig. The steemd program is open source on github. Someone with moderate to high c++ programming skills could adapt this code to run on GPU using something like CUDA or OpenCL. This could theoretically yield hash rates 10 fold and on a multi-high-end GPU rig you could have multiple GPU's on one system, yielding 600k-1200k.