Everyone optimizes for their own benchmarks. You can say it's dodgy, but that's really just an argument in favor of real-world tests instead of microbenchmarks like this one. You don't have to 'rig' a microbenchmark to come out the winner; you just pick the right microbenchmark, because it's not a real world scenario.
Given the lack of evidence to support actual cheating you should probably just apply occam's razor here and assume it's actually faster. Or you could use the dark, hidden secrets of 'view source' to read the JS yourself. It has comments!
making a benchmark specifically to be slower on your competitors browser? Little dodgy.
From everything I've read IE10 apparently is fast, and the numbers are believable from my experience doing similar things (web workers drawing fractal-like images on a canvas) but given that it's the only "pretty" benchmark in the lot, it just seems a little strange.
I think you misread my post. My point is that everyone optimizes their implementation so that their benchmarks run fast. Furthermore, people pick benchmarks that run fast on their implementation. Neither of these are a 'little dodgy': They are how benchmarks get used.
You might note that they make for bad science, but benchmarks tend not to get used in anything resembling a scientific comparison. Benchmarks get used for comparative testing (did we make thing X faster than it was before?) and to try and prove that your product is better than the competition (in which case much larger lies are going to get trotted out either way).
Given the lack of evidence to support actual cheating you should probably just apply occam's razor here and assume it's actually faster. Or you could use the dark, hidden secrets of 'view source' to read the JS yourself. It has comments!