"Beneath a Starry Sky" achievement bug

[Drifter Man]

I've just undeservedly earned the "Beneath a Starry Sky" achievement, although I only spent very little time outside at night. Unfortunately, I have no clear idea how it happened. I just went outside a few minutes before daybreak and when I returned inside a few minutes later, the achievement popped up at me from the corner.

I spent some time outside on the previous nights but no more than 1-2 hours after sunset. I slept for one hour in a snow shelter and for a few hours inside a cave, all during daytime. I didn't leave home (Upper Dam) before sunrise on those previous nights, at least I don't think so. I didn't do anything extraordinary, I've been living like this and doing things like this (except that shelter) for hundreds of days.

I can't find the usual output_log file... maybe the location has changed?