Oh dear, my apologies.
I can’t think of how stretching could physiological cause this to happen. Were you doing any A, V or fulcrum stretches? I suppose those could cause this, but I would imagine it would be quite a serious injury and you would have felt something. What is your routine?
From the picture it does look like, for some reason, there is a mid-section of skin on your penis that is a smaller circumference than the rest of the skin, causing a tightened ‘loop’ which is constricting the penis in that location and causing the house-glass effect.
My suggestion is to try and feel this area and grab opposing sides of the skin and try to manually stretch it, as I said before, for 10 minutes a day till it gets better. It’s relatively to easy to stetch skin, much easier than to increase penis size at least!