I've been playing for a few days and have some questions about events that happened to me.

When I first started the game, I came to the base, processed some signals and wanted to sleep, but couldn't because of some event. I sat on the bed and was scared about what could be outside. (Also, I've seen someone on the radar to the northeast.) After a while, I managed to sleep, and when I came out, some furniture was moved, and the table in the break room was missing (Screenshots below). What was that? I haven't found any events related to this.
I was upset about the furniture had been moved and was kinda scared it happened on the first day, so I started a new game.
Around day 10–14, I came into the kitchen upstairs and was about to use the microwave, when all of a sudden—BOOM—something exploded in the hallway and threw me away. (It was so unexpected I literally got goosebumps.) I wasn't hurt, but all my small stuff was scattered around the room. Same in the garage, upstairs storage, and main room. What was that? I tried to find the source of the explosion or some relevant event, but found nothing. Was it a bug?
And also, what is that sign? I saw it from the northern windmill (Last screenshot).