This seems really sloppy for China. Without further proof, I don't think it was the govt.
It's only "sloppy," though, when conceptualized as a MITM. China does have an extensive history of censoring access to sites, and recently censored access to GitHub entirely IIRC. It could be that they decided to block SSL access, but allow HTTP access, and this is how they implemented that.
I agree that this may be a further extending of the "New Years train ticket" block on Github.
It may also be new toying after the recent "experiment". Leaving Github without SSL inside China still makes trouble - China's insidious corruption at the very top is subtle, incremental small steps, all designed for the "long game".
It may also be raw mercantilism ... as with Google, Twitter, and Facebook long before this.
It should be 中国研究 but you said 中文研究, which means Chinese text research.
The level of sophistication that the GFW seems to be achieving is disturbing. We've had certificate attacks before, perhaps they are testing something out that will be deployed more broadly to solve there "gmail" problem?