What material is the pan made of? The outsides are pretty dark, which makes me think that they cooked quickly, causing the batter on the inside to rise more slowly and unevenly, so the raw batter on top flowed randomly to the side.
This has good information on how different materials affect muffin batter.
https://www.seriouseats.com/how-to-choose-the-best-muffin-pans-and-liners
I was wondering that too.I don't have any ideas, but that's definitely odd. It's like the top part was sheared and then slid.
House tilted?
Cold be, but the oven shelf is dead level.