I wouldn't say it was overblown, notice how everyone here is giving you the same roundabout answer?I think the drainage issue may be a bit overblown...maybe!
Poor drainage, lack of oxygen, or both.
Remember, warm water soaks in faster, and it was still sitting at the top of the pot long enough for you to grab your camera and take a picture. Not sure why, but the manure compost may be plugging up that "sandy loam" you mentioned.