History of Science and Mathematics moderator here. We've talked it over and have just sent the question back to Math Overflow (I closed it as off-topic on HSM, so that should bounce it back to MO automatically).
Over the last six years, we've had a lot of conversations with other STEM sites about their chosen policies on historical questions and what any migration process between those sites and HSM would look like. I think the big takeaway for me is that these questions really have to be dealt with on a case-by-case basis. What that means in practice is that meta discussions for each question can be quite valuable. There's often a fine line between questions that should be send to HSM and questions that should not - it's hard to capture the nuance of that in a few comments.
This case is a great example of that in action. I agree with this meta consensus - the fact that the key points are largely mathematical in nature indicates that Math Overflow is the better home. And, yes, appreciating the connections fully requires knowing some nontrivial mathematics.