In the image below, I have illustrated the interior of a bedroom with a slanted wall. On the slanted wall, I want to add a poster. Did I correctly use perspective here? Basically, I picked a point on the horizon that matched the top part of that slanted wall and used the same point to match the top of the poster.
Using the room itself, it would not be correct. Since there are two angles to use within the room, using those would provide more accurate perspective based upon the existing angles in the room (that I can see).
I have no idea how the horizon in your image was determined. There may be other aspects outside your posted image which warranted horizon placement. It is not impossible that you have the correct perspective if some factor merited the horizon placement where you have it.