Why would there be a warning for an "obstacle" 4km away from the end of the runway?

3800 - 2800 = 1km.

Did the plane skid for 1km before crashing into the obstacle?

Because the system is bureaucratic and stupid. Notices warning pilots about irrelevant obstacles are, literally, a meme. Example: https://www.reddit.com/r/flying/comments/wzsvru/the_notam_sy...

Almost anything that is 500m causes an obstacle notice to exist. There are tons of them and most mean nothing unless you’re flying an overweight small plane in the dark desert heat.