Seems like any post that gets edited gets it's timestamp updated to time of edit on main page listing. Just saw this post from 2012 at top of list due to a new answer. I sure don't remember this behavior in the past
As others have mentioned in the comments, the "interesting" tab on the home page has been around for a long time. Additionally, every non-Stack Overflow site in the network defaults to sorting by activity (in the reverse chronological order), so every Stack Exchange home page shows you questions that recently had something happen to them - typically an answer or an edit.
What you're looking for is the "newest" sub-tab on the "Questions" page instead. (Note that we also (somewhat unfortunately) remember which sub-tab on /questions you visit last and default to that on future visits.)
You can bookmark /questions?sort=newest, although you might want to further restrict that by tag since Stack Overflow gets thousands of questions every day.