Sorry to be a naysayer - But most of what you have posted is opinion and not facts. Do they look like they need vetrinary attention for any wounds/disease? Do they look sick? If it is snowing, I would HOPE they look shaggy! A small pen is no different to being stalled, except it isn't closed in.
Maybe it would have been worth having a chat to the guy - Oh hey, I noticed you got some horses, I have horses too! So on. You should try not to let any prejudices get in the way of your judgement.
I'd be pretty peeved if someone called AC on me bacsue my horse was in a yard, no shelter, and shaggy. My horses are always out with no shelter and shaggy in winter - And they are all fat and happy.
I have to agree with Wildspot here.
I had this happen to me first hand.....
Had an older rescue, that was skin and bones. She was on stall rest for about a month due to different ailments...but once she was well enough she was in a smaller corral which was located along side our driveway...(which happened to be visible from the road). She had already gained around 100lbs at this point, but still had LOADS of weight to go. We honestly thought she was going to die, the first month we had her.
The reason she was in a smaller corral was due to some hock and hoof injuries she had, and she wasn't to do a lot of moving around, but she still needed some excersice, as well as the grass, fresh air...seeing other horses, after being on stall rest for so long.
Well wouldnt you know, after about a week of her outside, we get the SPCA on our property a Lady had complained that our horse looked, boney, was in a small corral, and looked grubby and sad.
Uh...yeah...she was grubby...she only a month ago was a blink away from death!
This lady did not take the time to drive in our place to see all the other horses, fat, happy and healthy. She did not take the time to ask...Why?
I would of happily explained why.
Needless to say the SPCA left within minutes of arriving, and seeing our facility our horses, and what we were doing to aid the recovery of this mare.
So yeah, its best to get all the FACTS, and ask questions before jumping to conculsions!