It is surprising to me, for probably similar reasons that the authors expected. OSX has, for a long time, been the OS of choice for arguably the majority of developers that aren't developing specifically for windows (.NET etc). OSX has been obviously popular, though I recognise that in the last year there has been a trend of people complaining about OSX and threatening to leave.

I took the survey and I marked both OSX and Linux, because I deploy (local/docker remote/vm) to linux and spend quite some time in linux shells. I think it likely that a lot of windows users would do the same.

To be crystal clear, I wouldn't think that the majority of python developers are using linux as their primary development machine. I bet next year the survey will focus in on selecting primary OS as a choice.