First death of the year 😢

This burgeri has been in my care for a month or so. Most of my conos are dormant by now but this one hadn’t gone dormant yet. I noticed a few days ago a brown patch on it side and today it spread. I unposted it and realized the entire inside had turned rotten brown. First death this year. I’m kinda confused why it died because I haven’t watered it in weeks because I stopped watering for the year and it’s been dry. Maybe dry rot?