This question already has an answer here:
In 2017 the network decided to implement the HTTPS protocol, as was announced in Network-wide HTTPS: It's time. Although that post isn't completely marked as status-completed I think most, if not all, of that came through.
During that process there was a script that converted all links in posts from HTTP:// to HTTPS://, as you can see in the screenshot below (freehand circle mine).
Was this intended behaviour?
EDIT: I wrote a feature request to have the community user change these links as an answer to the original announcement.